Steven P. Arnoczky

Tendon-healing in a bone tunnel. A biomechanical and histological study in the dog.

Our study evaluated tendon-to-bone healing in a dog model. Twenty adult mongrel dogs had a transplantation of the long digital extensor tendon into a 4.8-millimeter drill-hole in the proximal tibial metaphysis. Four dogs were killed at each of five time-periods (two, four, eight, twelve, and twenty-six weeks after the transplantation), and the histological and biomechanical characteristics of the tendon-bone interface were evaluated. Serial histological analysis revealed progressive reestablishment of collagen-fiber continuity between the bone and the tendon. A layer of cellular, fibrous tissue was noted between the tendon and the bone, along the length of the bone tunnel; this layer progressively matured and reorganized during the healing process. The collagen fibers that attached the tendon to the bone resembled Sharpey fibers. High-resolution radiographs showed remodeling of the trabecular bone that surrounded the tendon. At the two, four, and eight-week time-periods, all specimens had failed by pull-out of the tendon from the bone tunnel. The strength of the interface was noted to have significantly and progressively increased between the second and the twelfth week after the transplantation. At the twelve and twenty-six-week time-periods, all specimens had failed by pull-out of the tendon from the clamp or by mid-substance rupture of the tendon. The progressive increase in strength was correlated with the degree of bone ingrowth, mineralization, and maturation of the healing tissue, noted histologically.

Microvasculature of the human meniscus

The microvascular anatomy of the medial and lateral menisci of the human knee was investigated in 20 cadaver specimens by histology and tissue clearing (Spalteholz) techniques. It was found that the menisci are supplied by branches of the lateral, medial, and middle genicular arteries. A perimeniscal capillary plexus originating in the capsular and synovial tissues of the joint supplies the peripheral 10-25% of the menisci. A peripheral, vascular, synovial fringe ex tends a short distance over both the femoral and tibial surfaces of the menisci but does not contribute any vessels to the meniscal stroma. The posterolateral aspect of the lateral meniscus adjacent to the popliteal tendon is devoid of penetrating peripheral vessels as well as a synovial fringe. The anterior and posterior horn attachments of the menisci are covered with vascular synovial tissue and appear to have a good blood supply.

The microvasculature of the meniscus and its response to injury An experimental study in the dog

The normal vascular anatomy of the menisci was inves tigated in five dogs by histology and tissue-clearing (Spalteholz) techniques. The vessels were found to originate in the perimeniscal capsular and synovial tis sues and penetrate the peripheral 25% of the meniscal tissues. The vascular response to complete midportion transection of the medial meniscus was evaluated in 15 dogs. This response originated from the peripheral synovial tissues and completely healed the lesion with fibrovascular scar tissue by 10 weeks. Longitudinal incisions in the avascular portion of the meniscus failed to heal. However, when these lesions were connected to the peripheral synovial tissues at their midportion by a vascular access channel, the entire lesion was healed with fibrovascular scar by 10 weeks.

The anatomy and histology of the inferior glenohumeral ligament complex of the shoulder

The gross and histologic anatomy of the inferior glenohumeral ligament was studied in 11 fresh frozen cadaver shoulders. Arthroscopic observations of the joint capsule through the normal range of motion re vealed that the inferior glenohumeral ligament is actually a complex of structures consisting of an anterior band, a posterior band, and an interposed axillary pouch. While these components of the inferior glenohumeral ligament complex were present in all 11 specimens, they were best demonstrated in some shoulders by placing the humeral head in internal or external rotation in varying degrees of abduction. Histologic examination of the joint capsule revealed that the anterior and posterior bands of the inferior glenohumeral ligament complex were readily identifiable as distinct structures comprised of thickened bands of well-organized colla gen bundles. Although slight variations were noted in the attach ment sites of the anterior and posterior bands to the glenoid, the inferior glenohumeral ligament complex was observed to attach to the humeral neck in one of two distinct configurations. A collar-like attachment, in which the entire inferior glenohumeral ligament complex attaches just inferior to the articular edge of the humeral head, was observed in six specimens. In the remaining five specimens, the attachment was in the shape of a V, with the anterior and posterior bands attaching adjacent to the articular edge of the humeral head and the axillary pouch attaching at the apex of the V distal to the articular edge. The orientation and design of the inferior glenohu meral ligament complex supports the functional con cept of this single structure as an important anterior and posterior stabilizer of the shoulder joint.

Anatomy of the anterior cruciate ligament.

The anterior cruciate ligament (ACL) is a multifascicular structure whose femoral and tibial attachments, as well as spatial orientation within the knee, are directly related to its function as a constraint of joint motion. The ACL is made up of multiple collagen bundles that give rise to the multifascicular nature of the ligament. This arrangement results in a different portion of the ligament being taut and therefore functional, throughout the range of motion. The ACL receives its blood supply from branches of the middle genicular artery, which from a vascular synovial envelope around the ligament. These periligamentous vessels penetrate the ligament transversely and anastomose with a longitudinal network of endoligamentous vessels. The body attachments do not contribute significantly to the vascularity of the ligament. The nerve supply to the ACL originates from the tibial nerve. Although the majority of fibers appear to have a vasomotor function, some fibers may serve a proprioceptive or sensory function.

Anterior cruciate ligament replacement using patellar tendon. An evaluation of graft revascularization in the dog.

UNLABELLEDnWe investigated the revascularization pattern of patellar tendon grafts used to replace the anterior cruciate ligament in thirty-six dogs by histological and tissue-clearing (Spalteholz) techniques. Initially the grafts were avascular, but by six weeks they were completely ensheathed in a vascular synovial envelope. The soft tissues of the infrapatellar fat pad, the tibial remnant of the anterior cruciate ligament, and the posterior synovial tissues contributed to this synovial vasculature. Intrinsic revascularization of the patellar tendon graft progressed from the proximal and distal portions of the graft centrally and was complete by twenty weeks. The tibial attachment of the patellar tendon graft did not contribute any vessels to the revascularization process. At one year, the vascular and histological appearance of the patellar tendon graft resembled that of a normal anterior cruciate ligament.nnnCLINICAL RELEVANCEnThe absence of perfused vessels within the patellar tendon graft immediately after transplantation within the knee joint and the failure of the osseous insertion of the graft to contribute vessels to the revascularization process suggest that although it is left attached at the tibia, the patellar tendon graft is essentially an avascular free graft at transplantation. The contribution of the soft tissues of the knee to the revascularization process of the graft suggests preservation and utilization of the infrapatellar fat pad and synovial tissue to optimize the grafts revascularization and ultimate viability.

Meniscal repair using an exogenous fibrin clot. An experimental study in dogs.

UNLABELLEDnTo evaluate the ability of a fibrin clot to stimulate and support a reparative response in the avascular portion of the meniscus, two-millimeter-diameter full-thickness lesions in the avascular portion of the medial meniscus of twelve adult dogs were filled with an exogenous fibrin clot that had been prepared from each animal. The healing response was then examined using histology and autoradiography with 35SO4 at intervals from one week to six months. The defects that had been filled with a fibrin clot healed through a proliferation of fibrous connective tissue that eventually modulated into fibrocartilaginous tissue. The fibrin clot appeared to act as a chemotactic and mitogenic stimulus for reparative cells and to provide a scaffolding for the reparative process. The origin of these reparative cells was not determined in this study, but they were thought to arise from the synovial membrane as well as the adjacent meniscal tissue. Control defects remained empty. While the reparative tissue was grossly and histologically different from the normal adjacent meniscal tissue, it was morphologically similar to the reparative tissue that was previously observed in the vascular area of the meniscus.nnnCLINICAL RELEVANCEnThe ability of an exogenous fibrin clot to stimulate and support a reparative response in the avascular portion of the meniscus may represent a potential method of avascular meniscal repair.

Anatomy, histology, and vascularity of the glenoid labrum. An anatomical study.

We studied the gross, histological, and vascular anatomy of the glenoid labrum in twenty-three fresh-frozen shoulders from cadavera to demonstrate its cross-sectional anatomy, its microvascularity, and its attachments. The superior and anterosuperior portions of the labrum are loosely attached to the glenoid, and the macro-anatomy of those portions is similar to that of the meniscus of the knee. The superior portion of the labrum also consistently inserts directly into the biceps tendon, while its inferior portion is firmly attached to the glenoid rim and appears as a fibrous, immobile extension of the articular cartilage. The arteries supplying the periphery of the glenoid labrum come from the suprascapular, circumflex scapular, and posterior circumflex humeral arteries. In general, the superior and anterosuperior parts of the labrum have less vascularity than do the posterosuperior and inferior parts, and the vascularity is limited to the periphery of the labrum. Vessels supplying the labrum originate from either capsular or periosteal vessels and not from the underlying bone.

Replacement of the anterior cruciate ligament using a patellar tendon allograft. An experimental study.

The anterior cruciate ligament of twenty-five adult dogs was replaced using fresh or deep-frozen patellar-tendon allografts. The morphology of these transplanted allografts was then evaluated using routine histological studies and a vascular-injection (Spalteholz) technique at various intervals from two weeks to one year postoperatively. The fresh patellar-tendon allografts incited a marked inflammatory and rejection response which was characterized by perivascular cuffing and lymphocyte invasion. Deep-frozen patellar-tendon allografts appeared to be benign within the joint and underwent alterations that were comparable with those observed in autogenous patellar-tendon grafts. These included avascular necrosis followed by revascularization and cellular proliferation. At one year, the gross and histological appearance of the patellar tendon allograft resembled that of a normal anterior cruciate ligament.

Freeze dried anterior cruciate ligament allografts Preliminary studies in a goat model

One ACL in each of 11 mature goats was replaced with a freeze dried bone-ACL-bone allograft. One year fol lowing implantation the goats had their knees evaluated biomechanically and for microvascularity and histologic changes. The reconstructed knees had a significantly greater total AP laxity (3.8 ± 0.6 mm) (mean and SEM) than the controls (1.0 ± 0.1 mm). Differences in primary AP laxity were responsible for 81 % of the difference in total laxity, with only a 0.4 mm difference in secondary laxity. Neutral stiffness in the reconstructive knee was 17% of control. while stiffness at 30 newtons (N) of anterior force was approximately 50% of controls. Lig ament stiffness in the linear region for the ACL allograft was 35% of the control value of 686 N/mm. The maxi mum load of the allografts was 571 ± 45 N, or 25% of the contralateral ACL control strength (2301 ± 155 N). Five of the seven allografts failed at the femoral inser tion. Both elongation (83%) and energy (21 %) to max imum load were less for allografts than controls. His tologic evaluation of the allografts revealed the pres ence of a regular oriented dense connective tissue which resembled a normal ligament. Microangiography revealed a periligamentous and endoligamentous vas cular pattern reminiscent of a normal ACL and complete revascularization of the bone plugs.