Anatomy, Biology and Biomechanics of Patellar Tendon Autograft Anterior Cruciate Ligament Reconstruction

Biomaterials developed for facilitating healing outcome after anterior cruciate ligament reconstruction: Efficacy, surgical protocols, and assessments using preclinical animal models

Anterior cruciate ligament (ACL) reconstruction is the recommended treatment for ACL tear in the American Academy of Orthopaedic Surgeons (AAOS) guideline. However, not a small number of cases failed because of the tunnel bone resorption, unsatisfactory bone-tendon integration, and graft degeneration. The biomaterials developed and designed for improving ACL reconstruction have been investigated for decades. According to the Food and Drug Administration (FDA) and the International Organization for Standardization (ISO) regulations, animal studies should be performed to prove the safety and bioeffect of materials before clinical trials. In this review, we first evaluated available biomaterials that can enhance the healing outcome after ACL reconstruction in animals and then discussed the animal models and assessments for testing applied materials. Furthermore, we identified the relevance and knowledge gaps between animal experimental studies and clinical expectations. Critical analyses and suggestions for future research were also provided to design the animal study connecting basic research and requirements for future clinical translation.

Do different tendons exhibit the same response following chronic exposure to statins?

Over the past few years, a number of cases of tendon injuries associated with statin therapy have been reported. In this study, we assessed whether statins can affect the extracellular matrix (ECM) of the deep digital flexor tendon (DDFT) and patellar tendon (PT). Wistar rats were assigned to groups treated with atorvastatin (A20, A80), treated with simvastatin (S20, S80), and control. Zymography, Western blotting for collagen I, non-collagenous proteins (NCP), glycosaminoglycans (GAGs), and hydroxyproline quantifications were performed. DDFT findings: NCP were increased in A20 and A80; higher concentration of hydroxyproline was found in S80; levels of GAGs was increased in all statin-treated groups; collagen I was increased in S80 and pro-MMP-2 activity was reduced in A80, S20, and S80. PT findings: NCP were reduced in A20, A80, and S80; GAGs was reduced in A80 and S20; collagen I was increased in A20 and pro-MMP-2 activity was reduced in the S20. Both the statins provoked marked changes in both tendons. All these changes may make the tendons more prone to microdamage and ruptures. Therefore, a better understanding of the behavior of the tendon ECM components under statin therapy may provide important insights into the mechanisms behind statin-induced tendon injuries.

Characteristics of inpatient anterior cruciate ligament reconstructions and concomitant injuries

PURPOSE

The purpose of this epidemiologic study was to quantify the incidence, expense, and concomitant injuries for anterior cruciate ligament reconstruction (ACLR) procedures in the USA from 2003 to 2011 that required an inpatient stay. It was hypothesized that the relative reported rates of concomitant knee injuries would be greater with the MCL and menisci compared to all other concomitant knee injuries.

METHODS

The National Inpatient Sample from 2003 to 2011 was retrospectively sampled using ICD-9-CM codes to identify ACLR patients and to extrapolate national averages.

RESULTS

Between the years of 2003-2011, an average of 9,037 ± 1,728 inpatient hospitalization included ACLRs, of which 4,252 ± 1,824 were primarily due to the ACLR. Inpatient visits primarily due to ACLR involved an average hospitalization of 1.7 ± 0.2 days and cost $30,118 ± 9,066 per patient. Knee injuries that were commonly reported along with inpatient ACLRs included medial meniscus damage (18.1 %), lateral meniscus damage (16.8 %), collateral ligament repairs (12.3 %), and medial collateral ligament strains (6.9 %). Prevalence of meniscus injuries was consistent across years, but MCL-related injuries increased over time.

CONCLUSIONS

ACLR-related inpatient hospitalizations account for approximately 7.1 % of the total ACLRs performed annually in the USA. Inpatient ACLR procedures continue to decrease in frequency; however, the mean cost per patient increased. Meniscus and collateral ligament injuries were the most commonly reported concomitant knee injuries. The clinical relevance of this investigation is that it informs, on a large clinical cohort of patients, the current state of incidence and expense for ACLR surgeries in an inpatient setting.

LEVEL OF EVIDENCE

Prognostic, retrospective study, Level II.

Effect of ACL graft material on anterior knee force during simulated in vivo ovine motion applied to the porcine knee: An in vitro examination of force during 2000 cycles

This study determined how anterior cruciate ligament (ACL) reconstruction affected the magnitude and temporal patterns of anterior knee force and internal knee moment during 2000 cycles of simulated gait. Porcine knees were tested using a six degree-of-freedom robot, examining three porcine allograft materials compared with the native ACL. Reconstructions were performed using: (1) bone-patellar tendon-bone allograft (BPTB), (2) reconstructive porcine tissue matrix (RTM), or (3) an RTM-polymer hybrid construct (Hybrid). Forces and moments were measured over the entire gait cycle and contrasted at heel strike, mid stance, toe off, and peak flexion. The Hybrid construct performed the best, as magnitude and temporal changes in both anterior knee force and internal knee moment were not different from the native ACL knee. Conversely, the RTM knees showed greater loss in anterior knee force during 2000 cycles than the native ACL knee at heel strike and toe off, with an average force loss of 46%. BPTB knees performed the least favorably, with significant loss in anterior knee force at all key points and an average force loss of 61%. This is clinically relevant, as increases in post-operative knee laxity are believed to play a role in graft failure and early onset osteoarthritis.

Effect of ACL graft material on joint forces during a simulated in vivo motion in the porcine knee: examining force during the initial cycles

This study compared three-dimensional forces in knees containing anterior cruciate ligament (ACL) graft materials versus the native porcine ACL. A six-degree-of-freedom (DOF) robot simulated gait while recording the joint forces and moments. Knees were subjected to 10 cycles of simulated gait in intact, ACL-deficient, and ACL-reconstructed knee states to examine time zero biomechanical performance. Reconstruction was performed using bone-patellar tendon-bone allograft (BPTB), reconstructive porcine tissue matrix (RTM), and an RTM-polymer hybrid (Hybrid). Forces and moments were examined about anatomic DOFs throughout the gait cycle and at three key points during gait: heel strike (HS), mid stance (MS), toe off (TO). Compared to native ACL, each graft restored antero-posterior (A-P) forces throughout gait. However, all failed to mimic normal joint forces in other DOFs. For example, each reconstructed knee showed greater compressive forces at HS and TO compared to the native ACL knee. Overall, the Hybrid graft restored more of the native ACL forces following reconstruction than did BPTB, while RTM grafts were the least successful. If early onset osteoarthritis is in part caused by altered knee kinematics, then understanding how reconstruction materials restore critical force generation during gait is an essential step in improving a patient's long-term prognosis.

Ligamentization of tendon grafts treated with an endogenous preparation rich in growth factors: gross morphology and histology

PURPOSE

To investigate whether the application of a particular platelet-rich plasma preparation rich in growth factors (PRGF) during anterior cruciate ligament (ACL) surgery gives a potential advantage for better tendon graft ligamentization.

METHODS

This study included 37 volunteers who underwent either conventional (control group, n = 15) or PRGF-assisted (n = 22) ACL reconstruction with an autogenous hamstring and required second-look arthroscopy to remove hardware or loose bodies, treat meniscal tears or plica syndrome, or resect cyclops lesions at 6 to 24 months after ACL surgery. The gross morphologies of the grafts were evaluated on second-look arthroscopy by use of the full arthroscopic score (0 to 4 points) to evaluate graft thickness and apparent tension (0 to 2 points) plus synovial coverage (0 to 2 points). At the same time, biopsy specimens were harvested uniformly from the grafted tendons. In these specimens the histologic transformation of the tendon graft to ACL-like tissue was evaluated by use of the Ligament Tissue Maturity Index, and a score to assess the progression of new connective tissue enveloping the graft was created by use of 3 criteria previously used to characterize changes during ligament healing: cellularity, vascularity, and collagen properties.

RESULTS

The overall arthroscopic evaluation of PRGF-treated grafts showed an excellent rating in 57.1% of the knees (score of 4) and a fair rating in 42.9% (score of 2 or 3). In contrast, evaluation of untreated grafts showed an excellent rating in 33.3% of the knees, a fair rating in 46.7%, and a poor rating in 20% (score of 0 or 1). Overall, arthroscopic evaluations were not statistically different between PRGF and control groups (P = .051). PRGF treatment influenced the histologic characteristics of the tendon graft, resulting in tissue that was more mature than in controls (P = .024). Histologically evident newly formed connective tissue enveloping the graft was present in 77.3% of PRGF-treated grafts and 40% of controls. The appearance of the connective tissue envelope changed with increasing time from surgery. On the basis of the histologic findings, we suggest that the remodeling of PRGF-treated grafts involves the formation of synovial-like tissue enveloping the graft. This tissue is eventually integrated in the remodeled tendon graft, conferring a similar appearance to the normal ACL.

CONCLUSIONS

The use of PRGF influenced the histologic characteristics of tendon grafts, resulting in more remodeling compared with untreated grafts. We have shown temporal histologic changes during the 6- to 24-month postoperative period of graft maturation, with newly formed connective tissue enveloping most grafts treated with PRGF.

LEVEL OF EVIDENCE

Level III, case-control study.

Complications of anterior cruciate ligament reconstruction with bone-patellar tendon-bone constructs: care and prevention

Rupture of the anterior cruciate ligament is a common injury. Correct diagnosis and patient selection, along with proper surgical technique, with careful attention to anatomic graft placement, followed by attention to proper rehabilitation, leads to predictably good to excellent results. This article reviews the recognition and avoidance of complications associated with bone-patellar tendon-bone constructs of anterior cruciate ligament reconstruction.