Biology of anterior cruciate ligament injury and repair: Kappa delta ann doner vaughn award paper 2013

Anterior cruciate ligament (ACL) injuries are currently treated by removing the injured ligament and replacing it with a tendon graft. Recent studies have examined alternative treatment methods, including repair and regeneration of the injured ligament. In order to make such an approach feasible, a basic understanding of ACL biology and its response to injury is needed. Identification of obstacles to native ACL healing can then be identified and potentially resolved using tissue engineering strategies-first, with in vitro screening assays, and then with in vivo models of efficacy and safety. This Perspectives paper outlines this path of discovery for optimizing ACL healing using a bio-enhanced repair technique. This journey required constructing indices of the functional tissue response, pioneering physiologically based methods of biomechanical testing, developing, and validating clinically relevant animal models, and creating and optimizing translationally feasible scaffolds, surgical techniques, and biologic additives. Using this systematic translational approach, "bio-enhanced" ACL repair has been advanced to the point where it may become an option for future treatment of acute ACL injuries and the prevention of subsequent post-traumatic osteoarthritis associated with this injury.

Use of a bioactive scaffold to stimulate anterior cruciate ligament healing also minimizes posttraumatic osteoarthritis after surgery

BACKGROUND

Although anterior cruciate ligament (ACL) reconstruction is the treatment gold standard for ACL injury, it does not reduce the risk of posttraumatic osteoarthritis. Therefore, new treatments that minimize this postoperative complication are of interest. Bioenhanced ACL repair, in which a bioactive scaffold is used to stimulate healing of an ACL transection, has shown considerable promise in short-term studies. The long-term results of this technique and the effects of the bioenhancement on the articular cartilage have not been previously evaluated in a large animal model.

HYPOTHESES

(1) The structural (tensile) properties of the porcine ACL at 6 and 12 months after injury are similar when treated with bioenhanced ACL repair, bioenhanced ACL reconstruction, or conventional ACL reconstruction, and all treatments yield results superior to untreated ACL transection. (2) After 1 year, macroscopic cartilage damage following bioenhanced ACL repair is similar to that in bioenhanced ACL reconstruction and less than in conventional ACL reconstruction and untreated ACL transection.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 64 Yucatan mini-pigs underwent ACL transection and randomization to 4 experimental groups: no treatment, conventional ACL reconstruction, bioenhanced ACL reconstruction using a bioactive scaffold, and bioenhanced ACL repair using a bioactive scaffold. The biomechanical properties of the ligament or graft were examined and macroscopic assessments of the cartilage surfaces were performed after 6 and 12 months of healing.

RESULTS

The structural properties (ie, linear stiffness, yield, and maximum loads) of the ligament after bioenhanced ACL repair were not significantly different from those in bioenhanced ACL reconstruction or conventional ACL reconstruction but were significantly greater than those in untreated ACL transection after 12 months of healing. Macroscopic cartilage damage after bioenhanced ACL repair was significantly less than that in untreated ACL transection and bioenhanced ACL reconstruction, and there was a strong trend (P = .068) for less macroscopic cartilage damage than in conventional ACL reconstruction in the porcine model at 12 months.

CONCLUSION

Bioenhanced ACL repair produces a ligament that is biomechanically similar to an ACL graft and provides chondroprotection to the joint after ACL surgery.

CLINICAL RELEVANCE

Bioenhanced ACL repair may provide a new, less invasive treatment option that reduces cartilage damage following joint injury.

Automatic determination of an anatomical coordinate system for a three-dimensional model of the human patella

Measuring the in vivo 3-D kinematics of the patella requires a repeatable anatomical coordinate system (ACS). The purpose of this study was to develop an algorithm to determine an ACS using the patella's unique morphology. An ACS was automatically constructed that aligned the proximal/distal (PD) axis with the posterior vertical ridge. Inter-subject ACS repeatability was determined by registering all patellae and their associated ACSs to a reference patella. The mean angle between the reference patella ACS and each subject's axes was less than 2.5° and the 95% CI was 1.0°-4.0°. Here, we presented an anatomical coordinate system that is independent of the observer's subjective judgement or orientation of the knee within the scanner.

Animal models of osteoarthritis: challenges of model selection and analysis

Osteoarthritis (OA) is the most common musculoskeletal disease, affecting millions of individuals worldwide. New treatment approaches require an understanding of the pathophysiology of OA and its biomechanical, inflammatory, genetic, and environmental risk factors. The purpose of animal models of OA is to reproduce the pattern and progression of degenerative damage in a controlled fashion, so that opportunities to monitor and modulate symptoms and disease progression can be identified and new therapies developed. This review discusses the features, strengths, and weaknesses of the common animal models of OA; considerations to be taken when choosing a method for experimental induction of joint degeneration; and the challenges of measuring of OA progression and symptoms in these models.

In Situ, noninvasive, T2*-weighted MRI-derived parameters predict ex vivo structural properties of an anterior cruciate ligament reconstruction or bioenhanced primary repair in a porcine model

BACKGROUND

Magnetic resonance imaging (MRI) is a noninvasive technology that can quantitatively assess anterior cruciate ligament (ACL) graft size and signal intensity. However, how those properties relate to reconstructed or repaired ligament strength during the healing process is yet unknown.

HYPOTHESIS

Magnetic resonance imaging-derived measures of graft volume and signal intensity are significant predictors of the structural properties of an ACL or ACL graft after 15 weeks and 52 weeks of healing.

STUDY DESIGN

Controlled laboratory study.

METHODS

The current data were gathered from 2 experiments evaluating ACL reconstruction and repair techniques. In the first experiment, pigs underwent unilateral ACL transection and received (1) ACL reconstruction, (2) ACL reconstruction with collagen-platelet composite (CPC), or (3) no treatment. The surgical legs were harvested after 15 weeks of healing. In the second experiment, pigs underwent ACL transection and received (1) ACL reconstruction, (2) ACL reconstruction with CPC, (3) bioenhanced ACL primary repair with CPC, or (4) no treatment. The surgical legs were harvested after 52 weeks. The harvested knees were imaged using a T2*-weighted 3-dimensional constructive interference in steady state (CISS) sequence. Each ligament was segmented from the scans, and the intra-articular volume and the median grayscale values were determined. Mechanical testing was performed to establish the ligament structural properties.

RESULTS

Volume significantly predicted the structural properties (maximum load, yield load, and linear stiffness) of the ligaments and grafts (R (2) = 0.56, 0.56, and 0.49, respectively; P ≤ .001). Likewise, the median grayscale values (ie, signal intensity) significantly predicted the structural properties of the ligaments and grafts (R (2) = 0.42, 0.37, and 0.40, respectively; P < .001). The combination of these 2 parameters in a multiple regression model improved the predictions (R (2) = 0.73, 0.72, and 0.68, respectively; P ≤ .001).

CONCLUSION

Volume and grayscale values from high-resolution T2*-weighted MRI scans are predictive of structural properties of the healing ligament or graft in a porcine model.

CLINICAL RELEVANCE

This study provides a critical step in the development of a noninvasive method to predict the structural properties of the healing ACL graft or repair. This technique may prove beneficial as a surrogate outcome measure in preclinical animal and clinical studies.

Pendulum mass affects the measurement of articular friction coefficient

Friction measurements of articular cartilage are important to determine the relative tribologic contributions made by synovial fluid or cartilage, and to assess the efficacy of therapies for preventing the development of post-traumatic osteoarthritis. Stanton's equation is the most frequently used formula for estimating the whole joint friction coefficient (μ) of an articular pendulum, and assumes pendulum energy loss through a mass-independent mechanism. This study examines if articular pendulum energy loss is indeed mass independent, and compares Stanton's model to an alternative model, which incorporates viscous damping, for calculating μ. Ten loads (25-100% body weight) were applied in a random order to an articular pendulum using the knees of adult male Hartley guinea pigs (n=4) as the fulcrum. Motion of the decaying pendulum was recorded and μ was estimated using two models: Stanton's equation, and an exponential decay function incorporating a viscous damping coefficient. μ estimates decreased as mass increased for both models. Exponential decay model fit error values were 82% less than the Stanton model. These results indicate that μ decreases with increasing mass, and that an exponential decay model provides a better fit for articular pendulum data at all mass values. In conclusion, inter-study comparisons of articular pendulum μ values should not be made without recognizing the loads used, as μ values are mass dependent.

Effects of suture choice on biomechanics and physeal status after bioenhanced anterior cruciate ligament repair in skeletally immature patients: a large-animal study

PURPOSE

The objective of this study was to assess the effect of absorbable or nonabsorbable sutures in bioenhanced anterior cruciate ligament (ACL) repair in a skeletally immature pig model on suture tunnel and growth plate healing and biomechanical outcomes.

METHODS

Sixteen female skeletally immature Yorkshire pigs were randomly allocated to receive unilateral, bioenhanced ACL repair with an absorbable (Vicryl) or nonabsorbable (Ethibond) suture augmented by an extracellular matrix-based scaffold (MIACH). After 15 weeks of healing, micro-computed tomography was used to measure residual tunnel diameters and growth plate status, and biomechanical outcomes were assessed.

RESULTS

At 15 weeks postoperatively, there was a significant difference in tunnel diameter with significantly larger diameters in the nonabsorbable suture group (4.4 ± 0.3 mm; mean ± SD) than in the absorbable group (1.8 ± 0.5 mm; P < .001). The growth plate showed a significantly greater affected area in the nonabsorbable group (15.2 ± 3.4 mm(2)) than in the absorbable group (2.7 ± 0.8 mm(2), P < .001). There was no significant difference in the linear stiffness of the repairs (29.0 ± 14.8 N/mm for absorbable v 43.3 ± 28.3 N/mm for nonabsorbable sutures, P = .531), but load to failure was higher in the nonabsorbable suture group (211 ± 121.5 N) than in the absorbable suture group (173 ± 101.4 N, P = .002). There was no difference between the 2 groups in anteroposterior laxity at 30° (P = .5117), 60° (P = .3150), and 90° (P = .4297) of knee flexion.

CONCLUSIONS

The use of absorbable sutures for ACL repair resulted in decreased physeal plate damage after 15 weeks of healing; however, use of nonabsorbable sutures resulted in 20% stronger repairs.

CLINICAL RELEVANCE

Choice of suture type for ACL repair or repair of tibial avulsion fractures may depend on patient skeletal age and size, with absorbable sutures preferred in very young, small patients at higher risk with physeal damage and nonabsorbable sutures preferred in larger, prepubescent patients who may place higher loads on the repair.

The effect of initial graft tension after anterior cruciate ligament reconstruction: a randomized clinical trial with 36-month follow-up

BACKGROUND

The initial graft tension applied at the time of anterior cruciate ligament (ACL) reconstruction alters joint contact and may influence cartilage health. The objective was to compare outcomes between 2 commonly used "laxity-based" initial graft tension protocols.

HYPOTHESES

(1) The high-tension group would have less knee laxity, improved clinical and patient-oriented outcomes, and less cartilage damage than would the low-tension group after 36 months of healing. (2) The outcomes of the high-tension group would be equivalent to those of a matched control group.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 1.

METHODS

Ninety patients with isolated unilateral ACL injuries were randomized to undergo ACL reconstruction using 1 of 2 initial graft tension protocols: (1) autografts tensioned to restore normal anterior-posterior (AP) laxity at the time of surgery (ie, low tension; n = 46) and (2) autografts tensioned to overconstrain AP laxity by 2 mm (ie, high tension; n = 44). Sixty matched healthy patients formed the control group. Outcomes were assessed preoperatively, intraoperatively, and at 6, 12, and 36 months after surgery.

RESULTS

No significant differences were found between the 2 initial graft tension protocols for any of the outcome measures at 36 months. However, there were differences when comparing the 2 treatment groups to the control group. On average, AP laxity was 2 mm greater in the ACL-reconstructed groups than in the control group (P < .007). International Knee Documentation Committee (IKDC) knee evaluation scores, peak isokinetic knee extension torques, and 4 of 5 Knee Osteoarthritis Outcome Scores (KOOS) were significantly worse than the control group (P < .001, P < .027, and P < .05, respectively). Short Form-36 Health Survey (SF-36) scores and reinjury rates were similar between groups at 36 months. Although there were significant changes in radiography and magnetic resonance imaging present in the ACL-reconstructed knees of both treatment groups, the magnitude was relatively small and likely clinically insignificant at 36 months.

CONCLUSION

Both laxity-based initial graft tension protocols produced similar outcomes without fully restoring joint function or patient-oriented outcomes (KOOS) when compared with the control group. There was minimal evidence of cartilage damage 36 months after surgery.

Cyclic loading increases friction and changes cartilage surface integrity in lubricin-mutant mouse knees

OBJECTIVE

To investigate the effects of lubricin gene dosage and cyclic loading on whole joint coefficient of friction and articular cartilage surface integrity in mouse knee joints.

METHODS

Joints from mice with 2 (Prg4(+/+)), 1 (Prg4(+/-)), or no (Prg4(-/-)) functioning lubricin alleles were subjected to 26 hours of cyclic loading using a custom-built pendulum. Coefficient of friction values were measured at multiple time points. Contralateral control joints were left unloaded. Following testing, joints were examined for histologic evidence of damage and cell viability.

RESULTS

At baseline, the coefficient of friction values in Prg4(-/-) mice were significantly higher than those in Prg4(+/+) and Prg4(+/-) mice (P < 0.001). Cyclic loading continuously increased the coefficient of friction in Prg4(-/-) mouse joints. In contrast, Prg4(+/-) and Prg4(+/+) mouse joints had no coefficient of friction increases during the first 4 hours of loading. After 26 hours of loading, joints from all genotypes had increased coefficient of friction values compared to baseline and unloaded controls. Significantly greater increases occurred in Prg4(-/-) and Prg4(+/-) mouse joints compared to Prg4(+/+) mouse joints. The coefficient of friction values were not significantly associated with histologic evidence of damage or loss of cell viability.

CONCLUSION

Our findings indicate that mice lacking lubricin have increased baseline coefficient of friction values and are not protected against further increases caused by loading. Prg4(+/-) mice are indistinguishable from Prg4(+/+) mice at baseline, but have significantly greater coefficient of friction values following 26 hours of loading. Lubricin dosage affects joint properties during loading, and may have clinical implications in patients for whom injury or illness alters lubricin abundance.

The impact of forced joint exercise on lubricin biosynthesis from articular cartilage following ACL transection and intra-articular lubricin's effect in exercised joints following ACL transection

OBJECTIVE

To evaluate the impact of forced joint exercise following acute knee injury on lubricin metabolism and its relationship to cartilage degeneration and to assess chondroprotection of a single-dose purified human lubricin injection in exercised injured joints.

METHODS

Anterior cruciate ligament transection (ACLT) was performed in rats with six experimental groups; 3-week post-ACLT, 3-week post-ACLT + exercise, 5-week post-ACLT, 5-week post-ACLT + exercise, and 5-week post-ACLT + exercise treated with intra-articular phosphate buffered saline (PBS) or lubricin. Joint exercise was achieved using a rotating cylinder at a speed of 6 rpm for 30 min daily, 5 days a week starting 1 week following surgery. Cartilage lubricin expression in injured joints was determined. Histological analyses included Safranin O/Fast Green, activated caspase-3, and lubricin mRNA in-situ hybridization. Assessment of cartilage damage was performed by osteoarthritis research society international (OARSI) modified Mankin scoring and urinary CTXII (uCTXII) levels.

RESULTS

At 3 weeks, lubricin expression in exercised ACLT joints was significantly (P < 0.001) lower compared to ACLT joints. The OARSI scores were significantly (P < 0.001) higher in the ACLT + exercise animals compared to ACLT animals at 5 weeks. Compared to 3-week ACLT, 3-week ACLT + exercise cartilage showed increased caspase-3 staining. Compared to ACLT + exercise and PBS-treated ACLT + exercise, lubricin intra-articular treatment resulted in a significant increase (P < 0.001) in cartilage lubricin gene expression and a reduction (P < 0.05) in uCTXII levels.

CONCLUSION

Joint exercise resulted in decreased lubricin cartilage expression, increased cartilage degeneration and reduced superficial zone chondrocyte viability in the ACLT joint. Intra-articular lubricin administration ameliorated cartilage damage due to exercise and preserved superficial zone chondrocytes' viability.

Effects of single-bundle and double-bundle ACL reconstruction on tibiofemoral compressive stresses and joint kinematics during simulated squatting

The purpose of this study was to compare tibiofemoral (TF) kinematics and TF compressive stresses between single bundle- (SB-) and double bundle-ACL reconstruction (DB-ACLR) during simulated squatting. Twelve matched pairs of fresh frozen cadaver knees were utilized. A simulated squat through 100° of knee flexion was performed in the ACL-intact joint. The ACL was transected and SB- and DB-ACLR procedures were performed in one knee of each pair. The squat was repeated. Knee kinematics were measured using a motion tracking system and the TF compressive forces were measured using thin film pressure sensors. The posterior shifts of the tibia for SB- and DB-ACLR knees were significantly greater than the ACL-intact condition for knee flexion angles 0° to 40° (p<.05). However, there was no difference between the SB- and DB-ACLR knees at any flexion angle (0° to 100°; p=.37). SB- and DB-ACLR knees had greater IE rotation than intact knees from 90° through 50° of flexion (p<.05), but not between 40° and full extension. There was no difference between SB- and DB-ACLR knees (p=.68). The TF compressive stresses of the DB-ACLR were significantly lower than intact for all angles except 10° (p=.06), whereas SB-ACLR knees did not differ from intact at flexion angles between 30° and 50° (p>.32). There were no significant differences between the two reconstruction conditions (p=.74). This study showed that there was no difference in the TF kinematics or compressive stresses between SB- and DB-ACLR, and only minor differences when compared to the intact state.

A comparative anatomical study of the human knee and six animal species

PURPOSE

Animal models are an indispensable tool for developing and testing new clinical applications regarding the treatment of acute injuries and chronic diseases of the knee joint. Therefore, the purpose of this study was to compare the anatomy of the intra-articular structures of the human knee to species commonly used in large animal research studies.

METHODS

Fresh frozen cow (n=4), sheep (n=3), goat (n=4), dog (n=4), pig (n=5), rabbit (n=5), and human (n=4) cadaveric knees were used. Passive range of motion and intra-articular structure sizes of the knees were measured, the structure sizes normalized to the tibial plateau, and compared among the species.

RESULTS

Statistically significant differences in the range of motion and intra-articular structure sizes were found among all the species. Only the human knee was able to attain full extension. After normalization, only the pig ACL was significantly longer than the human counterpart. The tibial insertion site of the ACL was split by the anterior lateral meniscus attachment in the cow, sheep, and pig knees. The sheep PCL had two distinct tibial insertion sites, while all the other knees had only one. Furthermore, only in human knees, both lateral meniscal attachments were located more centrally than the medial meniscal attachments.

CONCLUSIONS/CLINICAL RELEVANCE

Despite the relatively preserved dimensions of the cruciate ligaments, menisci, and intercondylar notch amongst human and animals, structural differences in the cruciate ligament attachment sites and morphology of the menisci between humans and animals are important to consider when selecting an animal model.

Activation of Indian hedgehog promotes chondrocyte hypertrophy and upregulation of MMP-13 in human osteoarthritic cartilage

OBJECTIVE

The objectives of this study were to (1) determine the correlation between osteoarthritis (OA) and Indian hedgehog (Ihh) expression, and (2) establish the effects of Ihh on expression of markers of chondrocyte hypertrophy and matrix metalloprotease (MMP)-13 in human OA cartilage.

DESIGN

OA cartilage and synovial fluid samples were obtained during total knee arthroplasty. Normal cartilage samples were obtained from intra-articular tumor resections, and normal synovial fluid samples were obtained from healthy volunteers and the contralateral uninjured knee of patients undergoing anterior cruciate ligament reconstruction. OA was graded using the Mankin score. Expression of Ihh in synovial fluid was determined by Western blot. Ihh, type X collagen and MMP-13 mRNA were determined by real time PCR. Protein expression of type X collagen and MMP-13 in cartilage samples was analyzed with immunohistochemistry. Chondrocyte size was measured using image analysis.

RESULTS

Ihh expression was increased 2.6 fold in OA cartilage and 37% in OA synovial fluid when compared to normal control samples. Increased expression of Ihh was associated with the severity of OA and expression of markers of chondrocyte hypertrophy: type X collagen and MMP-13, and chondocyte size. Chondrocytes were more spherical with increasing severity of OA. There was a significant correlation between Mankin score and cell size (r(2) = 0.80) and Ihh intensity (r(2) = 0.89). Exogenous Ihh induced a 6.8 fold increase of type X collagen and 2.8 fold increase of MMP-13 mRNA expression in cultured chondrocytes. Conversely, knockdown of Ihh by siRNA and Hh inhibitor cyclopamine had the opposite effect.

CONCLUSIONS

Ihh expression correlates with OA progression and changes in chondrocyte morphology and gene expression consistent with chondrocyte hypertrophy and cartilage degradation seen in OA cartilage. Thus, Ihh may be a potential therapeutic target to prevent OA progression.

Preventing friction-induced chondrocyte apoptosis: comparison of human synovial fluid and hylan G-F 20

OBJECTIVE

Symptomatic osteoarthritis (OA) is a common painful disease with limited treatment options. A rising number of patients with OA have been treated with intraarticular injections of hyaluronic acid, including the high-molecular-weight hylan G-F 20, which is injected following arthrocentesis. We investigated the effectiveness of hylan G-F 20 to lower coefficient of friction (COF) and prevent chondrocyte apoptosis in vitro.

METHODS

A disc-on-disc bovine cartilage bearing was used to measure the static and kinetic COF when lubricated with hylan G-F 20, human synovial fluid (HSF), and phosphate buffered saline (PBS). Following friction testing, we stained paraffin-embedded sections of these cartilage bearings for activated caspase-3, a marker of apoptosis.

RESULTS

Bearings lubricated with hylan G-F 20 had kinetic COF values that were similar to bearings lubricated with PBS, but significantly higher than those lubricated with HSF. There were no significant differences in static COF values in bearings lubricated with hylan G-F 20 as compared to PBS or HSF. However, bearings lubricated with HSF had significantly lower static COF values compared to bearings lubricated with PBS. The mean percentage of caspase-3-positive chondrocytes in the superficial and upper intermediate zones of bearings lubricated with hylan G-F 20 was significantly higher compared to that of bearings lubricated with HSF or unloaded controls, but significantly lower than in those lubricated with PBS.

CONCLUSION

These findings indicate that joint lubrication may prevent chondrocyte apoptosis by lowering the COF. Further, removal of synovial fluid prior to hylan G-F 20 injection may be detrimental to cartilage health.

Static and dynamic error of a biplanar videoradiography system using marker-based and markerless tracking techniques

The use of biplanar videoradiography technology has become increasingly popular for evaluating joint function in vivo. Two fundamentally different methods are currently employed to reconstruct 3D bone motions captured using this technology. Marker-based tracking requires at least three radio-opaque markers to be implanted in the bone of interest. Markerless tracking makes use of algorithms designed to match 3D bone shapes to biplanar videoradiography data. In order to reliably quantify in vivo bone motion, the systematic error of these tracking techniques should be evaluated. Herein, we present new markerless tracking software that makes use of modern GPU technology, describe a versatile method for quantifying the systematic error of a biplanar videoradiography motion capture system using independent gold standard instrumentation, and evaluate the systematic error of the W.M. Keck XROMM Facility's biplanar videoradiography system using both marker-based and markerless tracking algorithms under static and dynamic motion conditions. A polycarbonate flag embedded with 12 radio-opaque markers was used to evaluate the systematic error of the marker-based tracking algorithm. Three human cadaveric bones (distal femur, distal radius, and distal ulna) were used to evaluate the systematic error of the markerless tracking algorithm. The systematic error was evaluated by comparing motions to independent gold standard instrumentation. Static motions were compared to high accuracy linear and rotary stages while dynamic motions were compared to a high accuracy angular displacement transducer. Marker-based tracking was shown to effectively track motion to within 0.1 mm and 0.1 deg under static and dynamic conditions. Furthermore, the presented results indicate that markerless tracking can be used to effectively track rapid bone motions to within 0.15 deg for the distal aspects of the femur, radius, and ulna. Both marker-based and markerless tracking techniques were in excellent agreement with the gold standard instrumentation for both static and dynamic testing protocols. Future research will employ these techniques to quantify in vivo joint motion for high-speed upper and lower extremity impacts such as jumping, landing, and hammering.

Biomechanical outcomes after bioenhanced anterior cruciate ligament repair and anterior cruciate ligament reconstruction are equal in a porcine model

PURPOSE

The objective of this study was to compare the biomechanical outcomes of a new method of anterior cruciate ligament (ACL) treatment, bioenhanced ACL repair, with ACL reconstruction in a large animal model.

METHODS

Twenty-four skeletally immature pigs underwent unilateral ACL transection and were randomly allocated to receive bioenhanced ACL repair with a collagen-platelet composite, allograft (bone-patellar tendon-bone) reconstruction, or no further treatment (n = 8 for each group). The structural properties and anteroposterior laxity of the experimental and contralateral ACL-intact knees were measured 15 weeks postoperatively. All dependent variables were normalized to those of the contralateral knee and compared by use of generalized linear mixed models.

RESULTS

After 15 weeks, bioenhanced ACL repair and ACL reconstruction produced superior biomechanical outcomes to ACL transection. However, there were no significant differences between bioenhanced ACL repair and ACL reconstruction for maximum load (P = .4745), maximum displacement (P = .4217), or linear stiffness (P = .6327). There were no significant differences between the 2 surgical techniques in anteroposterior laxity at 30° (P = .7947), 60° (P = .6270), or 90° (P = .9008).

CONCLUSIONS

Bioenhanced ACL repair produced biomechanical results that were not different from ACL reconstruction in a skeletally immature, large animal model, although the variability associated with both procedures was large. Both procedures produced significantly improved results over ACL transection, showing that both were effective treatments in this model.

CLINICAL RELEVANCE

Bioenhanced ACL repair may one day provide an alternative treatment option for ACL injury.

Accelerated versus nonaccelerated rehabilitation after anterior cruciate ligament reconstruction: a prospective, randomized, double-blind investigation evaluating knee joint laxity using roentgen stereophotogrammetric analysis

BACKGROUND

The relationship between the biomechanical dose of rehabilitation exercises administered after anterior cruciate ligament (ACL) reconstruction and the healing response of the graft and knee is not well understood.

HYPOTHESIS

After ACL reconstruction, rehabilitation administered with either accelerated or nonaccelerated programs produces the same change in the knees' 6 degrees of freedom, or envelope, laxity values.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 1.

METHODS

Patients who underwent ACL reconstruction with a bone-patellar tendon-bone autograft were randomized to rehabilitation with either accelerated (19 week) or nonaccelerated (32 week) programs. At the time of surgery, and then 3, 6, 12, and 24 months later, the 6 degrees of freedom knee laxity values were measured using roentgen stereophotogrammetric analysis and clinical, functional, and patient-oriented outcome measures.

RESULTS

Eighty-five percent of those enrolled were followed through 2 years. Laxity of the reconstructed knee was restored to within the limits of the contralateral, normal side at the time of surgery (baseline) in all participants. Patients in both programs underwent a similar increase in the envelope of knee laxity over the 2-year follow-up interval (anterior-posterior translation 3.2 vs 4.5 mm, and coupled internal-external rotations 2.6° vs 1.9° for participants in the accelerated and nonaccelerated programs, respectively). Those who underwent accelerated rehabilitation experienced a significant improvement in thigh muscle strength at the 3-month follow-up (P < .05) compared with those who participated in nonaccelerated rehabilitation, but no differences between the programs were seen after this time interval. At the 2-year follow-up, the groups were similar in terms of clinical assessment, patient satisfaction, function, proprioception, and isokinetic thigh muscle strength.

CONCLUSION

Rehabilitation with the accelerated and nonaccelerated programs administered in this study produced the same increase in the envelope of knee laxity. A majority of the increase in the envelope of knee laxity occurred during healing when exercises were advanced and activity level increased. Patients in both programs had the same clinical assessment, functional performance, proprioception, and thigh muscle strength, which returned to normal levels after healing was complete. For participants in both treatment programs, the Knee Injury and Osteoarthritis Outcome Score (KOOS) assessment of quality of life did not return to preinjury levels.

Effect of muscle loads and torque applied to the tibia on the strain behavior of the anterior cruciate ligament: an in vitro investigation

BACKGROUND

Very little is known about the effects of applied torque about the long axis of the tibia in combination with muscle loads on anterior cruciate ligament biomechanics. The purpose of this study was to determine the effect of muscle contraction and tibial torques applied about the long axis of the tibia on anterior cruciate ligament strain behavior.

METHODS

Six cadaver knee specimens were used to measure the strain behavior of the anterior cruciate ligament. Internal and external axial torques were applied to the tibia when the knee was between 30° and 120° of flexion in combination with the conditions of no muscle load, isolated quadriceps load, and simultaneous quadriceps and hamstring loading.

FINDINGS

The highest anterior cruciate ligament strain values were measured when the muscles were not loaded, when the knee was at 120° of flexion, and when internal tibial torques were applied to the knee. During muscle loading the highest anterior cruciate ligament strain values were measured at 30° of flexion and then the strain values gradually decreased with increase in knee flexion. During co-contraction of the quadriceps and hamstring muscles the anterior cruciate ligament was unstrained or minimally strained at 60°, 90° and 120° of knee flexion.

INTERPRETATION

This study suggests that quadriceps and hamstring muscle co-contraction has a potential role in reducing the anterior cruciate ligament strain values when the knee is in deep flexion. These results can be used to gain insight into anterior cruciate ligament injury mechanisms and to design rehabilitation regimens.

Prevention of cartilage degeneration and gait asymmetry by lubricin tribosupplementation in the rat following anterior cruciate ligament transection

OBJECTIVE

To investigate whether cartilage degeneration is prevented or minimized in a rat model of anterior cruciate ligament (ACL) injury following a single dose-escalated intraarticular injection of lubricin derived from human synoviocytes in culture.

METHODS

Unilateral ACL transection (ACLT) of the right hind limb was performed in Lewis rats (n = 56). Control animals underwent a capsulotomy alone, leaving the ACL intact (n = 11). Intraarticular injections (50 μl/injection) of phosphate buffered saline (PBS; n = 14 rats) and human synoviocyte lubricin (1,600 μg/ml; n = 14 rats) were performed on day 7 postsurgery. Animals were killed on day 70 postsurgery. Histologic specimens were immunoprobed for lubricin and sulfated glycosaminoglycans. Urinary C-telopeptide of type II collagen (CTX-II) levels were measured on days 35 and 70 postsurgery. Hind limb maximum applied force was determined using a variable resistor walkway to monitor quadruped gait asymmetries.

RESULTS

Increased immunostaining for lubricin in the superficial zone and on the surface of cartilage was observed in lubricin-treated and control animals but not in PBS-treated or untreated animals with ACLT. On days 35 and 70 after surgery, urinary CTX-II levels in human synoviocyte lubricin-treated animals were lower than in untreated and PBS-treated animals (P < 0.005 and P < 0.001, respectively). Animals with ACLT treated with human synoviocyte lubricin and control animals distributed their weight equally between hind limbs compared to PBS-treated or untreated animals (P < 0.01).

CONCLUSION

Our findings indicate that a single intraarticular injection of concentrated lubricin following ACLT reduces type II collagen degradation and improves weight bearing in the affected rat joint. These findings support the practice of tribosupplementation with lubricin for retarding cartilage degeneration and possibly the development of posttraumatic osteoarthritis.

Contact area and pressure in suture bridge rotator cuff repair using knotless lateral anchors

PURPOSE

To evaluate whether the use of knotless lateral anchors in a suture bridge construct produces better contact area and pressure parameters than a suture bridge construct with standard lateral anchors that require knots or a double-row repair. The hypothesis was that knotless lateral anchors would produce better contact area and pressure parameters than the other two constructs.

METHODS

A total of fifteen matched pairs of cadaveric shoulders were divided into three groups. In Group 1, a suture bridge using knotless anchors for the lateral row was performed on five shoulders. A suture bridge using standard lateral row anchors that require knots was performed on the contralateral shoulders. In Group 2, suture bridge with knotless lateral row anchors was compared with double-row repair. In Group 3, suture bridge using standard lateral row anchors was compared with double-row repair. The contact conditions of the rotator cuff footprint were measured using pressure-sensitive film.

RESULTS

There were no statistically significant differences between any of the techniques regarding contact area F(2, 15.7) = 3.09, P = 0.07 or mean contact pressure F(2, 15.1) = 2.35, P = 0.12. A post hoc power analysis suggests differences between techniques are likely less than 91-113 mm(2) for area and 0.071-0.089 N for pressure.

CONCLUSIONS

The use of knotless anchors in the lateral row of a suture bridge repair did not increase the footprint contact area or contact pressure when compared to a suture bridge repair requiring knots laterally or to a double-row repair.

The use of magnetic resonance imaging to predict ACL graft structural properties

Magnetic resonance imaging (MRI) could potentially be used to non-invasively predict the strength of an ACL graft after ACL reconstruction. We hypothesized that the volume and T2 relaxation parameters of the ACL graft measured with MRI will predict the graft structural properties and anteroposterior (AP) laxity of the reconstructed knee. Nine goats underwent ACL reconstruction using a patellar tendon autograft augmented with a collagen or collagen-platelet composite. After 6 weeks of healing, the animals were euthanized, and the reconstructed knees were retrieved and imaged on a 3T scanner. AP laxity was measured prior to dissecting out the femur-graft-tibia constructs which were then tested to tensile failure to determine the structural properties. Regression analysis indicated a statistically significant relationship between the graft volume and the failure load (r(2)=0.502; p=0.049). When graft volume was normalized to the T2 relaxation time, the relationship was even greater (r(2)=0.687; p=0.011). There was a significant correlation between the graft volume and the linear stiffness (r(2)=0.847; p<0.001), which remained significant with T2 normalization (r(2)=0.764; p=0.002). For AP laxity at 30° flexion, there was not a significant correlation with graft volume, but there was a significant correlation with volume normalized by the T2 relaxation time (r(2)=0.512; p=0.046). These results suggest that MRI volumetric measures combined with graft T2 properties may be useful in predicting the structural properties of ACL grafts.

Reduced platelet concentration does not harm PRP effectiveness for ACL repair in a porcine in vivo model

Enhanced primary repair of the ACL using a collagen scaffold loaded with platelets has been shown to improve the functional healing of suture repair in animal models. In this study, our objectives were to determine if lowering the platelet concentration would reduce the structural properties of the repaired ACL and increase postoperative knee laxity. Eight Yucatan mini-pigs underwent bilateral suture repair. In one knee, the repair was augmented with a collagen scaffold saturated with platelet-rich plasma (PRP) containing five times the systemic baseline of platelets (5×) while the contralateral knee had a collagen scaffold saturated with PRP containing three times the systemic baseline of platelets (3×). After 13 weeks of healing, knee joint laxity and the structural properties of the ACL were measured. The 3× platelet concentration resulted in a 24.1% decrease in cellular density of the repair tissue (p < 0.05), but did not significantly decrease the structural properties [3× vs. 5×: 362 N vs. 291 N (p = 0.242) and 70 N/mm vs. 53 N/mm (p = 0.189) for the yield load and linear stiffness, respectively]. The 3× platelet concentration also did not significantly change the mean anteroposterior knee laxity at 30° and 90° of flexion [5× vs. 3×: 3.5 mm vs. 5.1 mm (p = 0.140), and 6.1 mm vs. 6.3 mm (p = 0.764)] but did result in a lower AP laxity at 60° [5× vs. 3×: 8.6 mm vs. 7.3 mm (p = 0.012)]. The decrease in platelet concentration from 5× to 3× to enhance suture repair of the ACL did not significantly harm the mechanical outcomes in this animal model.

Effects of supplemental intra-articular lubricin and hyaluronic acid on the progression of posttraumatic arthritis in the anterior cruciate ligament-deficient rat knee

BACKGROUND

Lubricin and hyaluronic acid lubricate articular cartilage and prevent wear. Because lubricin loss occurs after anterior cruciate ligament injury, intra-articular lubricin injections may reduce cartilage damage in the anterior cruciate ligament-deficient knee.

PURPOSE

This study was conducted to determine if lubricin and/or hyaluronic acid supplementation will reduce cartilage damage in the anterior cruciate ligament-deficient knee.

STUDY DESIGN

Controlled laboratory study.

METHODS

Thirty-six male rats, 3 months old, underwent unilateral anterior cruciate ligament transection. They were randomized to 4 treatments: (1) saline (phosphate-buffered saline [PBS]), (2) hyaluronic acid (HA), (3) purified human lubricin (LUB), and (4) LUB and HA (LUB+HA). Intra-articular injections were given twice weekly for 4 weeks starting 1 week after surgery. Knees were harvested 1 week after the final injection. Radiographs of each limb and synovial fluid lavages were obtained at harvest. Histologic analysis was performed to assess cartilage damage using safranin O/fast green staining. Radiographs were scored for the severity of joint degeneration using the modified Kellgren-Lawrence scale. Synovial fluid levels of sulfated glycosaminoglycan, collagen II breakdown, interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and lubricin were measured using enzyme-linked immunosorbent assay (ELISA).

RESULTS

Treatment with LUB or LUB+HA significantly decreased radiographic and histologic scores of cartilage damage (P = .039 and P = .015, respectively) when compared with the PBS and HA conditions. There was no evidence of an effect of HA nor was the LUB effect HA-dependent, suggesting that the addition of HA did not further reduce damage. The synovial fluid of knees treated with LUB had significantly more lubricin in the synovial fluid at euthanasia, although there were no differences in the other cartilage metabolism biomarkers.

CONCLUSION

Supplemental intra-articular LUB reduced cartilage damage in the anterior cruciate ligament-transected rat knee 6 weeks after injury, while treatment with HA did not.

CLINICAL RELEVANCE

Although longer term studies are needed, intra-articular supplementation (tribosupplementation) with lubricin after anterior cruciate ligament injury may protect the articular cartilage in the anterior cruciate ligament-injured knee.

Delay of 2 or 6 weeks adversely affects the functional outcome of augmented primary repair of the porcine anterior cruciate ligament

BACKGROUND

Enhanced primary anterior cruciate ligament repair, in which suture repair is performed in conjunction with a collagen-platelet composite to stimulate healing, is a potential new treatment option for anterior cruciate ligament injuries. Previous studies have evaluated this approach at the time of anterior cruciate ligament disruption.

HYPOTHESIS

Delaying surgery by 2 or 6 weeks would have a significant effect on the functional outcome of the repair.

STUDY DESIGN

Controlled laboratory study.

METHODS

Sixteen female Yorkshire pigs underwent staged, bilateral surgical anterior cruciate ligament transections. Anterior cruciate ligament transection was initially performed on 1 knee and the knee closed. Two or 6 weeks later, enhanced primary repair was performed in that knee while the contralateral knee had an anterior cruciate ligament transection and immediate repair. Biomechanical parameters were measured after 15 weeks in vivo to determine the effect of delay time relative to immediate repair on the healing response.

RESULTS

Yield load of the repairs at 15 weeks was decreased by 40% and 60% in the groups where repair was delayed for 2 and 6 weeks, respectively (P = .01). Maximum load showed similar results (55% and 60% decrease in the 2- and 6-week delay groups, respectively; P = .011). Linear stiffness also was adversely affected by delay (50% decrease compared with immediate repair after either a 2- or 6-week delay, P = .011). Anterior-posterior laxity after 15 weeks of healing was 40% higher in knees repaired after a 2-week delay and 10% higher in those repaired after a 6-week delay (P = .012) when tested at 30° of flexion, but was not significantly affected by delay when tested at 60° or 90° (P = .21).

CONCLUSION

A delay between anterior cruciate ligament injury and enhanced primary repair has a significant negative effect on the functional performance of the repair.

CLINICAL RELEVANCE

As future investigations assess new techniques of anterior cruciate ligament repair, the timing of the repair should be considered in the design and the interpretation of experimental studies.

The effect of skeletal maturity on functional healing of the anterior cruciate ligament

BACKGROUND

The effects of skeletal maturity on functional ligament healing are unknown. Prior studies have suggested that ligament injuries in skeletally mature animals heal with improved mechanical properties. In this study, we hypothesized that skeletally immature animals have improved functional healing compared with skeletally mature animals.

METHODS

Twenty-one Yucatan minipigs (eight juvenile, eight adolescent, and five adult animals) underwent bilateral anterior cruciate ligament transection. On one side, the ligament injury was left untreated to determine the intrinsic healing response as a function of age. On the contralateral side, an enhanced suture repair incorporating a collagen-platelet composite was performed. Biomechanical properties of the repairs were measured after fifteen weeks of healing, and histologic analysis was performed.

RESULTS

Anterior cruciate ligaments from skeletally immature animals had significantly improved structural properties over those of adult animals at three months after transection in both the untreated and repair groups. Use of the enhanced suture technique provided the most improvement in the adolescent group, in which an increase of 85% in maximum load was noted with repair. The repair tissue in the adult tissue had the highest degree of hypercellularity at the fifteen-week time point.

CONCLUSIONS

Functional ligament healing depends on the level of skeletal maturity of the animal, with immature animals having a more productive healing response than mature animals.