Bilateral Stance On Unstable Surface

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Witvrouw et al42 prospectively studied the risk factors for the development of anterior knee pain in the athletic population over a 2-year period. A significant difference was noted in the flexibility of the quadriceps and gastrocnemius muscles between the group of subjects who developed patellofemoral pain and the control group, suggesting that athletes exhibiting tightness of specific muscles may be at risk of the development of patellofemoral disorders.

In the upper extremity, it is common to see patients who present with tightness in the anterior structures, such as the pec-toralis musculature, and consequently exhibiting a protracted, forward head posture. This can lead to several shoulder pathologies, such as impingement due to the protracted and anteriorly tilted scapular position.43 Furthermore, the authors believe that loss of internal rotation (IR) in most throwers is due to posterior rotator cuff tightness and osseous adaptation44 and not from tightness of the posterior gleno-humeral joint.

RESTORATION OF NEUROMUSCULAR CONTROL

Early proprioception and kinesthesia exercises are important for patients returning to sporting activities. Basic exercises designed to enhance the athlete's ability to detect the joint position and movement in space are performed to establish a baseline of motor learning for further neuromuscular control exercises that will be integrated during the later phases of rehabilitation. Dynamic stability refers to the ability to stabilize a joint during functional activities to avoid injuries. This involves neuromuscular control and the efferent (motor) output to afferent (sensory) stimulation from the mechanoreceptors.

The emphasis of rehabilitation programs has shifted over the past several years to focus on restoring proprioception, dynamic stability, and neuromuscular control in patients. The neuromus-cular control system may have a critical effect on the prevention of serious knee injuries.45 Numerous authors have shown a decrease in proprioceptive and kinesthetic abilities following injury.46-50 Beard et al51 examined the effects of applying a 100-N anterior shear force on ACL-deficient knees and noted a deficit in reflexive activation of the hamstring musculature. Furthermore, Wojtys and Huston52 examined the neuromuscular deficits in 40 normal subjects and 100 ACL-deficient subjects. In response to an anteriorly directed tibial force, the ACL-defi-cient group showed deficits in muscle timing and recruitment order. Proprioceptive deficits following shoulder dislocation have also been noted.53

We routinely begin basic proprioceptive training during the early phases of rehabilitation, such as the second postoperative week following ACL reconstruction, pending adequate normalization of pain, swelling, and quadriceps control. Proprioceptive training initially begins with basic exercises such as joint repositioning and closed kinetic chain weight shifting. Furthermore, Chmielewski et al54 noted gait and weight-bearing drills are altered for several months following ACL injury.

Joint repositioning drills begin with the athlete's eyes closed. The rehabilitation specialist passively moves the extremity in various planes of motion, pauses, and then returns the extremity to the starting position. The patient is then instructed to actively reposition the extremity to the previous location. The rehabilitation specialist may perform these joint repositioning activities in variable degrees throughout the available ROM and notes the accuracy of the patient. Altering the patient's external stimulus such as vision and hearing may also provide increased challenge to the patient's proprioceptive system.

Weight shifts may be performed in the mediolateral direction and in diagonal patterns. Mini-squats are also performed early postoperatively. A force platform may be incorporated with weight shifts and mini-squats to measure the amount of weight distribution between the involved and uninvolved extremity (Fig. 11-4). Several authors have reported that an elastic bandage worn postoperatively has a positive impact on proprio-ception and joint position sense, and therefore our patients are encouraged to wear an elastic support wrap underneath their brace.55,56

As the patient advances, mini-squats are progressed onto an unstable surface such as foam or a tilt board. The patient is instructed to squat down to approximately 25 to 30 degrees and hold the position for 2 to 3 seconds while stabilizing the tilt

Supported Mini Squats

Figure 11-4 Mini-squats on a force platform (A) that can provide objective feedback of the amount of weight distributed between lower extremities (B) (Balance Trainer, Uni-Cam Inc., Ramsey, NJ).

Figure 11-4 Mini-squats on a force platform (A) that can provide objective feedback of the amount of weight distributed between lower extremities (B) (Balance Trainer, Uni-Cam Inc., Ramsey, NJ).

board. Wilk et al32 have shown the greatest amount of hamstring and quadriceps cocontraction occurred at approximately 30 degrees of knee flexion during the squat. Squats may be performed with the tilt board positioned in the mediolateral and anteroposterior directions. Wojtys et al57 have shown that muscular contraction can decrease the anterior and posterior laxity in the knee joint by 275% to 450%. Also, Baratta et al58 have shown an increased risk of ligamentous injury in knees with quadriceps to hamstring muscle strength imbalances. Thus, we believe by improving neuromuscular coactivation, stability is enhanced.

Unstable Surface
Figure 11-5 A and B, Lateral lunges using a sport cord onto an unstable surface.

As proprioception is advanced, drills to encourage preparatory agonist-antagonist coactivation during functional activities are incorporated. These dynamic stabilization drills for the lower extremity begin with single-leg stance on flat ground and unstable surfaces, cone stepping, and lateral lunge drills. The patient may perform forward, backward, and lateral cone stepover drills to facilitate gait training, enhance dynamic stability, and train the hip to help control forces at the knee joint. The patient is instructed to raise the knee up to the level of the hip and step over a series of cones, landing with a slightly flexed knee. These cone drills may also be performed at various speeds to train the lower extremity to dynamically stabilize with different amounts of momentum.

Lateral lunges are also performed with the patient instructed to lunge to the side, landing on a slightly flexed knee and holding that position for 1 to 2 seconds before returning to the start position. We use a functional progression for the lateral lunges: straight-plane lateral lunges are performed first, progressing to multiple-plane/diagonal lunges, lateral lunges with rotation, and finally lateral lunges onto foam (Fig. 11-5). As the patient progresses, concentration may be distracted by including a ball toss with any of these exercises to challenge the preparatory stabilization of the lower extremity with minimal conscious awareness.

Single-leg balance exercises are progressed by altering the patient's center of gravity and incorporating movement of the upper extremity and the uninvolved lower extremity. The patient stands on a piece of foam with the knee slightly flexed and performs random flexion, extension, abduction, adduction, and diagonal movement patterns of the upper extremity while holding weighted balls and maintaining control of the knee joint (Fig. 11-6). The uninvolved lower extremity may also be moved

Single Leg Stance Foam
Figure 11-6 Single-leg balance on an unstable surface while incorporating alternating upper extremity movements with a weighted ball to alter the patient's center of gravity.

in the anteroposterior or mediolateral directions while maintaining control of the joint. Finally, both upper extremity and lower extremity movements may be combined. The patient again stabilizes the flexed knee on a piece of foam as the upper extremity moves forward with simultaneous extension of the lower extremity. This movement is followed by the upper extremity extending while the lower extremity moves forward. These single-leg balance drills are used with extremity movement to provide mild variations of the patient's center of gravity, thus altering the amount of dynamic stabilization needed as well as recruiting various muscle groups to provide the majority of neuromuscular control. Medicine balls of progressive weight may be incorporated to provide further challenge to the neuro-muscular control system.

Perturbation training may also be incorporated. Fitzgerald et al28 examined the efficacy of perturbation training in the rehabilitation program of ACL-deficient knees. The authors reported that perturbation training resulted in more satisfactory outcomes and lessened the frequency of subsequent giving way episodes in ACL-deficient knees. We incorporate perturbations while the patient performs double- or single-leg balance on a tilt board. While flexing the knee to approximately 30 degrees, the patient stabilizes the tilt board with an isometric hold at 30 degrees of flexion and throws and catches a lightweight medicine ball. The patient is instructed to stabilize the tilt board in reaction to the sudden outside force produced by the weighted ball. The rehabilitation specialist may also provide manual perturbations by striking the tilt board with his or her foot to create a sudden disturbance in the static support of the lower extremity, requiring the patient to stabilize the tilt board with dynamic muscular contractions (Fig. 11-7). Perturbations may also be performed during this drill by tapping the patient at the hips to provide proximal and distal perturbation forces.

Rehabilitation Device Sports

Figure 11-7 Single-leg balance on a tilt board while the patient tosses a ball against a rebound device. The rehabilitation specialist can create a perturbation by striking the board.

Upper Extremity Plyometric Exercises

Figure 11-8 Upper extremity plyometrics.

Figure 11-7 Single-leg balance on a tilt board while the patient tosses a ball against a rebound device. The rehabilitation specialist can create a perturbation by striking the board.

Figure 11-8 Upper extremity plyometrics.

Exercises such as balance beam walking, lunges onto an unstable surface, and step-up exercises while standing on an unstable surface are also used to strengthen the knee musculature while requiring the muscles located proximally and distally within the kinetic chain to stabilize and allow coordinated functional movement patterns. For a complete description and progression to neuromuscular control drills for the ACL patient, Wilk et al59-61 have published several articles.

Plyometric jumping drills may also be performed to facilitate dynamic stabilization and neuromuscular control of the knee joint. Plyometric exercises use the muscle's stretch-shortening properties to produce maximal concentric contraction following a rapid eccentric loading of the muscle tissues.61,62 Plyometric training is used to train the extremities to produce and dissipate forces to avoid injury (Fig. 11-8).

Hewett et al63 examined the effects of a 6-week plyometric training program on the landing mechanics and strength of female athletes. The authors reported a 22% decrease in peak ground reaction forces and a 50% decrease in the abduction/adduction moments at the knee during landing. Also, significant increases in hamstring isokinetic strength, hamstring-to-quadriceps ratio, and vertical jump height were reported.

Using the same plyometric program, Hewett et al64 prospec-tively analyzed the effect of neuromuscular training on serious knee injuries in female athletes. The authors reported a statistically significant decrease in the amount of knee injuries in the trained group compared to the control group.

The final aspect of rehabilitation regarding neuromuscular control involves enhancing muscular endurance. Proprioceptive and neuromuscular control has been shown to diminish once muscular fatigue occurs.65-67 Exercises such as bicycling, stair climbing, and elliptical machines may be used for long durations to increase endurance as well as high repetition, low weight

Figure 11-9 Rhythmic stabilization to promote cocontraction of the rotator cuff.

resistance strengthening. Additionally, we frequently recommend performing neuromuscular control drills toward the end of a treatment session, after cardiovascular training. This type of training is performed to challenge the neuromuscular control of the knee joint when the dynamic stabilizers have been adequately fatigued.

The enhancement of neuromuscular control is equally important in the upper extremity, and many of the previously mentioned techniques can also be applied to the upper extremity. The excessive mobility and compromised static stability observed within the glenohumeral joint often result in numerous injuries to the capsulolabral and musculotendinous structures of the shoulder. Efficient dynamic stabilization and neuromuscular control of the glenohumeral joint is necessary for athletes to avoid injuries during competition.19

Dynamic stabilization exercises for the upper extremity also begin with baseline proprioception and kinesthesia drills to maximize the athlete's awareness of joint position and movement in space. In addition to joint repositioning and closed kinetic chain drills, rhythmic stabilizations are incorporated to facilitate cocontraction of the rotator cuff and dynamic stability of the glenohumeral joint. This exercise involves alternating isometric contractions designed to promote cocontraction and basic reactive neuromuscular control (Fig. 11-9). These dynamic stabilization techniques may be applied as the athlete progresses to provide advancing challenge to the neuromuscular control system. As the athlete progresses, it is necessary to train the upper extremity to provide adequate dynamic stabilization in response to sudden forces, particularly at end ROM (Fig. 1110). We refer to this as reactive neuromuscular control.

EMPHASIS ON THE ENTIRE KINETIC CHAIN

Rehabilitation must be focused on not only regaining strength and neuromuscular control of the affected joint, but also include attention to the surrounding areas. For example, neuromuscular control of the shoulder involves stability of not only the gleno-humeral joint but also the scapulothoracic joint. The scapula serves to provide a stable base of support for muscular attachment and dynamically positions the glenohumeral joint during upper extremity movement. Scapular strength and stability are essential to proper function of the glenohumeral joint. Therefore, isotonic strengthening and dynamic stabilization of the scapular musculature should also be included in rehabilitation programs for the athlete's shoulder to ensure proximal stability. Furthermore, the core of the body should be emphasized to enhance scapular control.

Additionally, altered forces at the knee joint may be the result of several biomechanical faults, both distal and proximal in the kinetic chain. These include rearfoot and tibial rotation distally and femoral rotation, hip control, and core stability proximally.

Bilateral Hip Rotation Exercise Bed

Figure 11-10 A, Manual resistance during side-lying external resistance; the rehabilitation specialist resisted both external rotation and retraction of the scapula. B, Rhythmic stabilizations may also be performed at end range.

Figure 11-10 A, Manual resistance during side-lying external resistance; the rehabilitation specialist resisted both external rotation and retraction of the scapula. B, Rhythmic stabilizations may also be performed at end range.

Rhythmic Stabilization Sidelying

Figure 11-11 Abdominal exercises on a Swiss ball while holding a Figure 11-12 Proprioceptive neuromuscular facilitation exercise while weighted ball. standing on a piece of foam. This exercise incorporates strengthening, neuromuscular control, and core stabilization while simulating the stance position of baseball pitching.

Figure 11-11 Abdominal exercises on a Swiss ball while holding a Figure 11-12 Proprioceptive neuromuscular facilitation exercise while weighted ball. standing on a piece of foam. This exercise incorporates strengthening, neuromuscular control, and core stabilization while simulating the stance position of baseball pitching.

The senior author of this chapter (K.W.) believes that the way to control varus and valgus at the tibiofemoral joint is either proximally (through pelvic and hip control) and/or distally with foot mechanics (e.g., controlling hyperpronation). Thus, we emphasize hip rotation strengthening exercises and foot biome-chanical correction.

Core stabilization drills are used to further enhance proximal stability with distal mobility of the extremities. Core stabilization is used based on the kinetic chain concept where imbalance within any point of the kinetic chain may result in pathology throughout. Movement patterns, such as throwing, require a precise interaction of the entire body kinetic chain to perform efficiently. An imbalance of strength, flexibility, endurance, or stability may result in fatigue, abnormal arthrokinematics, and subsequent compensation. Core stabilization is progressed using a multiphase approach, progressing from baseline core and trunk strengthening to intermediate core strengthening (Fig. 11-11) with distal mobility to advanced stabilization in sport-specific movement patterns (Fig. 11-12).

Also, during rehabilitation, it is important not to neglect the uninjured extremity. Studies have pointed to a crossover effect when the contralateral extremity is exercised, which may result in improvements in proprioception and strength.68-71 Preliminary studies at our center have shown a decrease in proprioception of the uninvolved extremity following ACL injury. This has also been reported with unilateral ankle sprains. It appears that the neuromuscular control system may have a certain amount of central mediating function that may be receptive to bilateral training techniques. Thus, when rehabilitating a patient with a joint injury, the rehabilitation specialist must consider the patient performing either bilateral exercises or unilateral reciprocal exercises (Fig. 11-13).

GRADUAL RECONDITIONING THROUGH APPLIED LOADS AND STRESSES

Rehabilitation must be performed in a gradual manner. Tissues are best reconditioned through progressive loading and stressing. The rehabilitation process involves a progressive application of therapeutic exercises designed to gradually increase function in the athlete. As previously discussed, an overaggressive approach early within the rehabilitation program may result in increased pain, inflammation, and effusion. This simple concept may also be applied to the progression of strengthening exercises, proprioception training, neuromuscular control drills, functional drills, and sport-specific training. For example, exercises such as weight shifts and lunges are progressed from straight plane anteroposterior or mediolateral directions to involve multiplane and rotational movements. Two-legged exercises, such as leg press, knee extension, balance activities, and plyometric jumps, are progressed to single-leg exercises. Thus, the progression through the postoperative rehabilitation program involves a gradual progression of applied and functional stresses. This progression is used to provide a healthy stimulus for healing tissues while ensuring that forces are gradually applied without causing damage. This ensures that the patient has ample time to develop the neuromuscular control and dynamic stabilization needed to perform these drills.

Bilateral Stance

Figure 11-13 Examples of exercises performed bilaterally, the standing "full can" exercise (A) and forward lunging onto a box (B).

Figure 11-13 Examples of exercises performed bilaterally, the standing "full can" exercise (A) and forward lunging onto a box (B).

GRADUAL RETURN TO FUNCTIONAL ACTIVITIES

Following the successful completion of a rehabilitation program, the athlete must begin a gradual return to sport activities. Interval sport programs (ISPs) are designed to gradually return motion, function, and confidence to the athlete after injury or surgery by slowly progressing through graduated sport-specific activities.72 The goal of this phase is to gradually and progressively increase the functional demands on the athlete to return the patient to full, unrestricted sport or daily activities. The criteria established before a patient's return to sport activities are (1) full functional ROM, (2) adequate static stability, (3) satisfactory muscular strength and endurance (Fig. 11-14), (4) adequate dynamic stability, and (5) a satisfactory clinical examination. Once these criteria are successfully met, the patient may initiate a gradual return to sport activity in a controlled manner. Healing constraints based on surgical technique and fixation, as well as the patient's tissue status, should be considered before a functional program can be initiated.

The interval sport program is set up to minimize the chance of reinjury and emphasize precompetition warm-up and stretching. Because there is an individual variability in all athletes, there is no set timetable for completion of the program. Variability will exist based on the skill level, goals, and injury of each athlete. ISPs may be developed based on the specific sport and stresses observed during these athletic activities. For example, overhead athletes perform an interval throwing program that begins with a limited amount of throws using a flat-ground long-toss program. As the distance of throws is progressed from 45, 60, 90, and 120 feet, the athlete may progress to begin throwing from a mound.

Again, a gradual approach is applied by limiting the amount of throws and the intensity of throws is progressed.

Other goals of this phase are to maintain the patient's muscular strength, dynamic stability, and functional motion established in the previous phase. A stretching and strengthening program should be performed on an ongoing basis to maintain and continue to improve on these goals. The rate of progression with functional activities is dictated by the patient's unique tolerance to the activities. Exercise must be performed at a tolerable level without overstressing the healing tissues; this is referred to as the patient's envelope of function.

The athlete's return to sport-specific drills progresses through a series of transitional drills designed to progressively challenge the neuromuscular control system. Pool running is performed prior to flat-ground running, backward and lateral running is performed prior to forward running, plyometrics are performed prior to running and cutting drills, and finally sport-specific agility drills are performed. The integration of functional activities is necessary to train the injured patient to perform specific movement patterns necessary for everyday activities. The intention of sport-specific training is to simulate the functional activities associated with sports while incorporating peripheral afferent stimulation with reflexive and preprogrammed muscle control and coactivation. Many of the drills, such as cone drills, lunges with sport cord, plyometrics drills, and the running and agility progression may be modified based on the specific functional movement patterns associated with the patient's unique sport. Some of the sport-specific running and agility drills incorporated include side shuffle, cariocas, sudden starts and stops, 45-degree cutting, 90-degree cutting, and various combinations of the previous drills. The specific movement patterns learned throughout the rehabilitation program are integrated to provide challenge in a controlled setting. These drills are performed to train the neuromuscular control system to perform during competition in a reflexive pattern to prevent injuries.

CONCLUSIONS

The rehabilitation process is based on our knowledge of the basic science of injury and tissue healing as well as an understanding of the general principles discussed in this chapter. Team communication and the gradual application of these principles in a well-designed rehabilitation program based on the individual needs of each patient are essential to ensure successful results. The goal of this chapter was to discuss current concepts in the rehabilitation process.

The ultimate goal of the rehabilitation process is not getting the patient or athlete back to work or sport as fast as possible, but rather returning the patient to function when it is safe and appropriate. For example, returning someone to running or jumping while the patient exhibits a femoral bone bruise can lead to long-term articular cartilage problems. The ultimate goal of rehabilitation is a healthy, asymptomatic patient 5 to 10 years after surgery, not just at 6 months.

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68. Kannus P, Alosa D, Cook L, et al: Effect of one-legged exercise on the strength, power and endurance of the contralateral leg. A randomized, controlled study using isometric and concentric isokinetic training. Eur J Appl Physiol Occup Physiol 1992;6:117-126.

69. Nagel MJ, Rice MS: Cross-transfer effects in the upper extremity during an occupationally embedded exercise. Am J Occup Ther 2001 ;55: 317-323.

70. Stromberg BV: Contralateral therapy in upper extremity rehabilitation. Am J Phys Med 1986;65:135-143.

71. Stromberg BV: Influence of cross-education training in postoperative hand therapy. South Med J 1988;81:989-991.

72. Reinold MM, Wilk KE, Reed J, et al: Interval sport programs: Guidelines for baseball, tennis, and golf. J Orthop Sports Phys Ther 2002;32:293-298.

CHAPTER 12

Safety Issues for Musculoskeletal Allografts

Craig S. Mauro, Jeffrey A. Rihn, and Christopher D. Harner

In This Chapter

Bacterial infection Viral infection Immunologic concerns Tissue bank regulation Tissue procurement Aseptic tissue processing Secondary tissue sterilization Tissue storage

INTRODUCTION

• Musculoskeletal allograft tissue has become increasingly popular, with approximately 350,000 allografts distributed in 1990 and 875,000 in 2001.1

• The advantages of allograft tissue include decreased operating time, no donor-site morbidity, and increased availability of tissue in complex multiligament or revision surgery.

• Clinical studies have demonstrated results comparable with those of autograft tissue.2-4

• Allograft tissue is associated with the risk of disease transmission and the potential for immune reaction.

• We describe the reported cases of infection and the risk for immune reaction from allograft tissue transplantation before outlining the current state of tissue bank regulation and tissue procurement, processing, sterilization, and storage.

BACTERIAL INFECTION

In the December 7, 2001, Morbidity and Mortality Weekly Report, the Centers for Disease Control and Prevention (CDC) described four cases of septic arthritis following anterior cruciate ligament (ACL) reconstruction using allograft tissue, bringing this issue to national attention.5 Each of the patients in this series underwent ACL reconstruction using a bone-patellar tendon-bone (BPTB) allograft. The allografts used in two of the patients were supplied from one Texas tissue bank and had been harvested from a common donor. The grafts had been irradiated and processed according to standard procedures. The cultures from the surgical site infections of these patients grew Pseudomonas aeruginosa that had indistinguishable genotypic patterns. The grafts used in the other two patients in this series also were supplied from another common donor and processed through one Florida tissue bank. These allografts had not received terminal sterilization with gamma irradiation.

Subsequently, in March 2002, the CDC reported having identified 26 patients who had developed allograft-associated infections.6 This investigation was prompted by the death of a 23-year-old man who received a femoral condyle bone-cartilage allograft and died on postoperative day 4 with blood cultures growing Clostridium sordellii.7,s The allograft implanted into this patient was from a donor whose tissues were transplanted into eight other patients. Of these patients, only one other patient, who had received a femoral condyle allograft and a meniscus allograft, developed an infection. His cultures also grew C. sor-dellii, but he was treated with ampicillin-sulbactam and recovered. Of these 26 cases identified by the CDC, 13 were infections with Clostridium spp. and 14 were associated with a single tissue processor. Eleven of the 13 allografts associated with the Clostridium spp. infections were processed by a single tissue bank. Eight of the 13 allografts associated with the Clostridium spp. infections were tendons used for ACL reconstructions. The allografts in remaining five patients with Clostridium spp. infections were from femoral condyles (two), bone (two), and meniscus (one).

Following the report by the CDC describing the allograft associated Clostridium spp. infections, Kainer et al9 further traced these infected tissues to tissue banks and reported their findings in 2004. They identified 14 patients who developed culture-proven Clostridium spp. infection of a surgical site within 1 year of allograft implantation between 1998 and 2002. These 14 allografts were from nine donors and were processed by a single tissue bank. The authors estimated the rates of Clostridium spp. infection in patients receiving an allograft from the implicated tissue bank in 2001 to be 0.12% for all sports-medicine tissues. Barbour and King10 had previously described four of these cases in detail, demonstrating the morbidity caused by such an infection.

The CDC again reported on a case of infection following ACL reconstruction with allograft tissue in December 2003.11 In this case, the affected individual's cultures grew Streptococcus pyogenes (group A streptococcus). This bacterium had been identified in the preprocessing cultures of the tissues recovered from the donor. Since all postprocessing tissue cultures were negative, the tissues were distributed. Tendon allografts from the donor had also been implanted in five other patients, but there have been no reports of infection in these patients.

VIRAL INFECTION

Transmission of viral infections through musculoskeletal allograft tissue has been occasionally reported in the literature. There have been several cases of transmission of hepatitis C virus (HCV) and one unidentified case of hepatitis in 1954.12-16 In 2003, the CDC

reported on the most recent case of HCV transmission, which occurred through a patellar tendon allograft from a donor in the window period between infection and detectable HCV-antibody response.15 The other tissues from this donor included 44 organs and tissues that had been transplanted into 40 recipients. Thirty-two patients received tissues and five probable cases of HCV infection developed: in all three recipients of tendon with bone, in one of three recipients of tendon, and in one of three recipients of saphenous vein.

Two cases of human immunodeficiency virus (HIV),17-19 and one case of human T-lymphotrophic virus (HTLV)20 transmission through allograft tissue have been reported to date. The first case of HIV transmission reported involved a patient who received bone from a femoral head of an unscreened donor for a spinal fusion in 1984.17 The second case is one of a young male donor who was screened and found to be seronegative by enzyme-linked immunosorbent assay HIV antibody testing after being shot to death in 1985.18,19 Fifty-two of his tissues were transplanted into recipients, and three patients who received tissue from a femoral head or a BPTB ultimately tested positive for the HIV antibody. The case of HTLV transmission was through a femoral head allograft in 1991.20 Except for the most recent case of hepatitis C transmission, the viral transmissions occurred before current serologic tests were available and before the implementation of guidelines for donor screening for viruses and bacteria.

IMMUNOLOGIC CONCERNS

Animal and clinical studies of menisci, tendons, cartilage, and bone have demonstrated a localized immune response associated with allograft transplantation.21-23 Rodeo et al23 demonstrated the presence of histocompatibility antigens on the donor menis-cal surface at the time of transplantation and immunoreactive lymphocytes in the meniscus or synovial tissue of the recipient at follow-up. This response did not, however, affect the clinical outcome of these patients. Friedlaender et al22 confirmed the immunogenicity of bone allografts, and Vasseur et al21 identified the presence of antibodies to donor leukocyte antigens in the synovial fluid of dogs following allograft ACL transplantation. Although a histologically evident immune response seems to be elicited by all allograft material, this immune response does not appear to affect clinical outcome.

TISSUE BANK REGULATION

A tissue bank is an organization that provides donor screening, recovery, processing, storage, and/or distribution of allograft tissue. The first tissue bank, a dedicated bone bank, was des cribed by Inclan24 in 1942. A 2001 report by the Department of Health and Human Services (HHS) Office of Inspector

General identified 154 tissue banks.25 Regulation of tissue banks has developed concurrently with their increasing number.

Currently, there are three levels of tissue bank regulation:

the U.S. Food and Drug Administration (FDA), the American Association of Tissue Banks (AATB), and the state governments.

The FDA seeks to prevent communicable diseases by requiring donor screening and testing. Further, the FDA began inspecting tissue banks in 1993 and has the power to halt operations at a bank, recall tissue, and punish owners/operators. The 2001

HHS report identified that the FDA had never inspected at least

36 of the 154 identified tissue banks. Further, of the 118 banks that had been inspected, 68 had been inspected only once. The limitations of the FDA oversight identified in the report were identification of banks, because banks were not required to register with the FDA, and insufficient funds to expand the inspection program.25

In January 2004, the FDA Good Tissue Practices broadened the scope of tissue establishments, as regulations became effective requiring tissue bank registration with the agency and disclosure of each cell or tissue produced.26 The FDA's new comprehensive framework also proposed establishment of donor suitability criteria for donors of human cellular and tissue-based products and requirement of manufacturers to follow current good tissue practices.

In May 2004, the donor suitability regulations requiring human cell, tissue, and cellular and tissue-based product establishments to screen and test cell and tissue donors for risk factors for, and clinical evidence of, relevant communicable disease agents and diseases became effective.27 Further, in May 2005, the FDA began requiring human cell, tissue, and cellular and tissue-based product establishments to follow current good tissue practices.28 This requirement governs the methods used in, and the facilities and controls used for, the manufacture of human cell, tissue, and cellular and tissue-based products; record keeping; and the establishment of a quality program. With this regulation the FDA also issued new regulations pertaining to labeling, reporting, inspections, and enforcement that apply to manufacturers of certain human cell, tissue, and cellular and tissue-based products.

The AATB is a not-for-profit organization that was founded in 1976 to facilitate the provision of transplantable cells and tissues of uniform high quality in quantities sufficient to meet national needs. The AATB began offering inspection and accreditation of tissue banks in 1986. Following an application process, banks may undergo an on-site inspection of facilities and operations, including record keeping, quality control, quality assurance, donor and tissue suitability determination, and safety. Tissue banks may receive accreditation for their operations including retrieval, processing, storage, and/or distribution of tissue. Currently, the AATB also offers a program of certification of tissue bank personnel through an examination that tests candidates on their knowledge in all areas of tissue banking. The AATB currently has 85 members on its accredited bank list. Tissue banks are not required to apply for accreditation by the AATB, and nonaccredited tissue banks are under no obligation to meet the policies or standards of the AATB.

New York and Florida are the only two states that require licensure and inspection of tissue banks. They address issues such as tissue procurement process, tracking practices, emergency procedures, equipment standards, conflict of interest, laboratory testing, and disposition of unused tissue. In addition, these states require banks to report adverse incidents. Less stringent requirements exist in California, Georgia, and Maryland, where tissue banks must be licensed by the state. There is no licensure or inspection of tissue banks at the state level in the other 45 states.

TISSUE PROCUREMENT

Tissue procurement is coordinated through the nationwide Organ Procurement and Transplantation Network, to which organ procurement organizations belong. Organ procurement organizations are responsible for first evaluating potential donors and discussing donation with family members, and, ultimately arranging for the surgical removal of donated organs. These

Box 12-1 Window Periods for Detection of Antibodies

Standard

With Nucleic Acid Amplification

Human immunodeficiency virus 22 days Hepatitis B 56 days Hepatitis C 70 days

7-12 days 41-50 days 10-29 days

organizations are also important for the procurement of musculoskeletal tissue because they refer potential donors to tissue banks. The tissue bank is then responsible for the procurement process.

The FDA requires that tissue donors must be screened for HIV, hepatitis B virus (HBV), HCV, Treponema pallidum (syphilis), HTLV I and II, and human transmissible spongiform encephalopathy, including Creutzfeldt-Jakob disease. This screening is accomplished through a medical history and physical examination. The FDA also requires serologic testing for HIV HBV, HCV, and Treponema pallidum, and, in viable, leukocyte-rich tissues, cytomegalovirus and HTLV I and II. One limitation with the screening process is the window period, the time period between which an individual is infected with a virus and the virus becomes detectable by screening tests. Traditionally, the detection of antibodies to a virus marked the end of the window period. This period is about 22 days for HIV, 56 days for HBV and 70 days for HCV29 The window period may be shortened by using nucleic acid amplification testing, but it still remains 7 to 12 days for HIV 41 to 50 days for HBV, and 10 to 29 days for HCV (Box 12-1).29

Once the donor is deemed free of risk factors, tissue processing begins. Despite this screening, contamination inherent to the graft may be the result of occult infection in the donor or postmortem invasion by organisms from the donor's gastrointestinal or respiratory tract. The latter risk increases with time postmortem, so most banks have a 24-hour postmortem limit during which tissue may be procured.30 However, this regulation is variable and difficult to monitor. Following recovery, the tissues are transported under conditions designed to maintain tissue integrity.

ASEPTIC TISSUE PROCESSING

Aseptic tissue processing is the most common method of preparation employed by tissue banks to minimize contamination of tissue. The technique does not remove contaminants; rather, the process seeks to prepare the tissue without adding further contaminants to it. The CDC stressed this fact in the December 2001 Morbidity and Mortality Weekly Report, stating, "Although aseptic processing avoids contamination of tissue at the tissue bank, it does not eliminate contamination originating from the donor that might be inherent to the graft."5 The technique removes only surface lipids and blood and does not penetrate the tissue.

Following aseptic processing but before the application of antibiotics, disinfectants, or sterilizing agents, swab culturing for bacteria and fungi is performed. The results are maintained in the donor's records and are reviewed before the tissue is released. However, the sensitivity of swab cultures of allograft tissue has been reported to be as low as 10%, suggesting inadequacy of this instrument of allograft contamination iden tification.31 Following culturing, some tissue processors apply antiseptic and/or antibiotic solutions. These solutions may kill some surface microbes, but they do not kill viruses and do not fully penetrate the tissue.

SECONDARY TISSUE STERILIZATION

Sterilization is a process that results in the killing or inactivation of all life forms. The American National Standard Institute and the Association for the Advancement of Medical Instrumentation define sterility in terms of a sterility assurance level. They have established the industry standard sterility assurance level for medical devices as 10-6, which means that the probability of a single viable organism being present on an item is one in one million after the item has undergone a terminal sterilization process validated to that level.32

Secondary tissue sterilization is used because of the limitations described in donor screening, graft harvesting, and micro-bial testing. Ideally, this terminal sterilization would eliminate all pathogens without affecting the biologic and biomechanical properties of the tissues. However, such ideal sterilization, as conventionally performed on medical devices, may not truly exist for tissues. With tissue sterilization, this balance between tissue sterility and tissue properties must always be considered. Further, most sterilization techniques are validated by a log-reduction assay that uses spiked tissue samples. These samples are immersed into known concentrations of bacterial and/or viral cultures before being treated and then recultured for the presence of the organisms. Systemically infected tissue is not routinely tested for validation, possibly compromising the validity of this assay for testing allograft tissue sterilization techniques.

Traditionally, ethylene oxide and gamma irradiation have been used in the tissue sterilization process. Recently, low-temperature chemical sterilization methods have also been developed.

Ethlyene Oxide

Ethylene oxide has historically been the most common method of tissue sterilization. It causes DNA and RNA dysfunction through alkylation of purine and pyrimidine moieties. The solution kills bacteria, fungi, and spores and preserves the tissue strength and biocompatibility, although biocompatibility may be dose dependent. However, it does not kill viruses and has a limited ability to fully penetrate tissue. Further, reports have noted that ethylene oxide and its byproducts (ethylene glycol and ethylene chlorohydrin) may be toxic, which prompted the FDA to regulate residual levels of ethylene oxide and its by-products.33 Since ethylene oxide has been shown to incite a chronic synovitis, it has largely been abandoned as a sterilizing agent for tissue used for reconstruction of intra-articular liga-ments.33 Consequently, most tissue banks use other methods of tissue sterilization.

Gamma Irradiation

Gamma irradiation is typically delivered to tissue at levels of 1.0 to 3.5 mrad.30 It fully penetrates tissue, preserves biocompati-bility, and kills bacteria, fungi, and spores at relatively low doses (1.5 to 2.0 mrad). Further, gamma irradiation kills viruses in a dose-dependent manner. Studies suggest that doses greater than 2.5 mrad are required to inactivate HIV in allograft tissue.34,35

Gamma irradiation also decreases tissue strength in a dose-dependent manner.36-38 Doses as low as 2.0 mrad have been shown to reduce the structural properties of BPTB allograft.37,38

In 1995, Fideler et al37 demonstrated a dose-dependent effect of irradiation on both the structural and mechanical properties of a human BPTB allograft. A dose of 2.0 mrad resulted in a statistically significant reduction in four of seven biomechanical parameters tested, including modulus and maximum stress to failure of the tissue. All seven parameters were reduced in a dose-dependent fashion after 3.0 and 4.0 mrad of irradiation. More recently, Curran et al38 studied the effect of 2.0 mrad on the cyclic and failure properties of human BPTB allograft. This low dose of irradiation resulted in a 27% increase in elongation after cyclic loading and a 20% decrease in strength compared to nonirradiated grafts. The authors believed that these effects may be detrimental to graft function and could lead to graft failure when used to reconstruct the ACL. They suggested the use of nonirradiated rather than irradiated allograft to avoid such problems.

It is unknown whether this alteration in biomechanical properties has an effect on clinical outcome. Rihn et al39 recently presented a study comparing the clinical outcome of patients who underwent ACL reconstruction with irradiated allograft BPTB with those who underwent ACL reconstruction with autograft BPTB. The allograft BPTB grafts used had been irradiated with 2.5 mrad prior to distribution from the tissue bank. They found both the patient-reported and objective outcomes of irradiated BPTB allograft ACL reconstruction were statistically and clinically similar to those obtained using autograft BPTB. They concluded that irradiation may be used as a means of sterilization of allograft BPTB without compromising the clinical outcome of ACL surgery, but the optimal dose of irradiation necessary for true sterilization remains unclear. Therefore, the dose of gamma irradiation must be considered when using this method of tissue sterilization.

Low Temperature Chemical Sterilization

The newest methods developed for tissue sterilization use low temperature chemical sterilization. These techniques are designed to kill spores but preserve the biomechanical integrity of the tissue. Allowash XG (Lifenet, Virginia Beach, VA), BioCleanse (Regeneration Technologies Incorporated, Alachua, FL), Tutoplast (Tutogen Medical, Inc., West Paterson, NJ), and NovaSterilis (NovaSterilis, Lansing, NY) are examples of these processes. The Allowash formula combines biologic detergents, alcohol, and hydrogen peroxide with ultrasonics, centrifugation, and negative pressure. The BioCleanse tissue sterilization process relies on the low-temperature chemicals to completely penetrate the tissue. The Tutoplast process uses solvent dehydration with acetone baths and low-dose gamma irradiation. The NovaSterilis process uses supercritical CO2 to kill microorganisms through transient acidification by carbonic acid formation. Initial reports suggest that these chemical sterilization techniques are effective in sterilizing tissue and have no effect on the biomechanical properties of tissue. However, further evaluation of these techniques is warranted to confirm their effectiveness and identify any risks.

Other techniques currently being used for tissue sterilization include the Clearant Process (Clearant, Inc., Los Angeles, CA) and peracetic acid-ethanol. The Clearant Process uses a process of high-dose irradiation under conditions optimized to minimize damage to the tissue. Free radicals and reactive oxygen species are secondary products of standard gamma irradiation techniques that are thought to cause the deleterious biomechanical effects. The Clearant Process seeks to minimize this secondary chemistry. The tissues are incubated in a solution containing

Box 12-2 Tissue Storage Options

Deep-freezing: tissue frozen to -80°C, most common method, grafts stored 3-5 years

Freeze-drying: moisture removed, vacuum packaged, can be stored 3-5 years (room temperature)

Cryopreservation: controlled-rate freezing, preserves cells, grafts stored 10 years radioprotectants, including propylene glycol and dimethyl sulfoxide. They are then dehydrated to 8% residual moisture before being irradiated with 5.0 mrad at -65°C. The process has been shown to have no effects on the mechanical properties of tendon and bone.40 Peracetic acid-ethanol has been used for more than 20 years in Europe to sterilize bone allografts. Recently, it has been applied to BPTB grafts without any apparent effect on the biomechanical properties of the tissue.

TISSUE STORAGE

The current methods of allograft tissue storage include deepfreezing, freeze-drying, and cryopreservation. Each of these techniques may be used for storage of ligament and meniscal allografts. Deep-freezing is the most widely used storage method for ligament and meniscal allografts, entailing simply freezing the tissue to -80°C. The grafts typically can be stored for 3 to 5 years. In the freeze-drying process, moisture is removed from the tissue and the graft is vacuum packaged. It may be stored at room temperature for 3 to 5 years but requires rehydration before implantation. Deep-freezing and freeze-drying allograft

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