David L. Butler

Biomechanical analysis of human ligament grafts used in knee-ligament repairs and reconstructions

Virtually all types of collagenous tissues have been transferred in and around the knee joint for intra-articular and extra-articular ligament reconstructions. However, the mechanical properties (in particular, strength) of such grafts have not been determined in tissues from young adult donors, where age and disuse-related effects have been excluded. To provide this information, we subjected ligament graft tissues to high-strain-rate failure tests to determine their strength and elongation properties. The results were compared with the mechanical properties of anterior cruciate ligaments from a similar young-adult donor population. The study indicated that some graft tissues used in ligament reconstructions are markedly weak and therefore are at risk for elongation and failure at low forces. Grafts utilizing prepatellar retinacular tissues (as in certain anterior-cruciate reconstructions) and others in which a somewhat narrow width of fascia lata or distal iliotibial tract is utilized are included in this at-risk group. Wider grafts from the iliotibial tract or fascia lata would of course proportionally increase ultimate strength. The semitendinosus and gracilis tendons are stronger, having 70 and 49 per cent, respectively, of the initial strength of anterior cruciate ligaments. The bone-patellar tendon-bone graft (fourteen to fifteen millimeters wide, medial or central portion) was the strongest, with a mean strength of 159 to 168 per cent of that of anterior cruciate ligaments. Patellar tendon-bone units, based on grip-to-grip motions, were found to be three to four times stiffer than similarly gripped anterior cruciate ligaments, while gracilis and semitendinosus tendon preparations had values that were nearly identical to those of anterior cruciate ligaments.(ABSTRACT TRUNCATED AT 250 WORDS)

Arthroscopy in acute traumatic hemarthrosis of the knee. Incidence of anterior cruciate tears and other injuries.

In a prospective study, all injured knees that had traumatic hemarthrosis and absent or negligible instability on clinical examination underwent arthroscopy and examination under anesthesia. Eighty-five knees (eighty-three patients) were examined over a 125-week period. Some degree of disruption of the anterior cruciate ligament was found in sixty-one (72 per cent) of the knees (a partial tear in 28 per cent and a complete tear in 44 per cent), frequently associated with an injury of varying severity to other joint structures. These included minor ligament sprains without laxity in 41 per cent, a major associated ligament injury in 21 per cent, meniscal tears in 62 per cent (partial in 30 per cent and complete in 70 per cent), and a femoral chondral fracture or surface defect in 20 per cent. A popping sensation at injury occurred in 33 per cent of knees with a normal anterior cruciate ligament and in 36 per cent of those with a disruption. One-third of the knees had no to slight pain at the time of injury. The anterior drawer test without anesthesia was positive in only 24 per cent of the knees with a torn anterior cruciate ligament. We concluded that: (1) a traumatic hemarthrosis indicates a significant knee injury; (2) examination under anesthesia plus arthroscopy allows a more accurate diagnosis of injury to joint structures; and (3) such data are required for a rational treatment program to be outlined.

Ligamentous and capsular restraints preventing straight medial and lateral laxity in intact human cadaver knees.

In this study, we determined which hgaments and capsular structures resist medial and lateral opening of the joint space in cadaver knees during clinical testing for straight medial and lateral laxity. Restraining function was recorded as the per cent contribution of each structure in resisting the force applied by the examiner. In sixteen cadaver knees tested at 5 and 25 degrees of flexion from full hyperextension, the collateral ligaments provided the primary restraint (greater than one-half of the total) at both flexion angles. At 5 degrees, the posterior part of the capsule and the cruciate ligaments were important secondary restraints. As flexion increased, the posterior part of the capsule became slack, causing a marked decrease in its restraining action. The middle one-third of the medial and lateral halves of the capsule, traditionally considered important, provided little restraining force. The iliotibial tract and the pophiteus musculotendinous unit provided little passive restraint. However, a force applied to either the ihiotibial band or the biceps tendon, to simulate muscle tension, produced an additional restraint that in vivo presumably would protect the lateral ligaments and capsule. Using an instrumented kinematic chain to determine the three-dimensional joint motion in six knees during testing for straight varus-valgus laxity by the maneuvers used clinically, we found that axial rotation of the tibia occurred that may be misinterpreted as medial or lateral joint opening. When just the medial or the lateral collateral ligament (the primary re* Read in part at the Annual Meetings of the Orthopaedic Research Society. Dallas. Texas. February 21. 1978. and San Francisco, California, February 20. 1979. r This work was supported in part by Grant ROl AM 21 172 from the National Institutes of Health, Grant 239 from the Orthopaedic Research and Education Foundation, and Air Force Contract F33615-C05 1 1. 4: Department of Orthopaedic Surgery. College of Medicine, 231 Bethesda Avenue, Cincinnati. Ohio 45267. straints) was sectioned, only a three to five-millimeter increase in joint opening occurred. This increase was small because only low forces were applied during the clinical examination and the secondary restraints blocked further opening even though the primary restraint was disrupted. Near full extension, the secondary restraints almost completely blocked opening of the joint after sectioning of the collateral ligaments. CLINICAL RELEVANCE: With knowledge of the hierarchy of restraining moments contributed by the medial and lateral ligament and capsular structures and an appreciation of the rotatory movements of the knee that may occur during tests for straight varusvalgus laxity, both diagnosis and treatment can be more precise. In the past, most assessments of ligament function have been based on the changes in laxity observed after cutting selected ligaments3”5’32 or else on the injury patterns associated with observed clinical laxities’M13”4’”” 20,24,25,28 As a result, confusion and disagreement persist as to the ligament injuries associated with specific laxities. Often in clinical practice the ligaments that may be involved are just listed. Accurate diagnosis and optimum treatment require that the function of the ligaments in resisting joint opening be understood and ranked in order of importance. Recently we described a new method for determining the restraining force provided by each ligament and capsulan structure5’6’9. This method allows the ligaments to be ranked in order of importance based on the per cent of the total restraining force that each provides. In addition, the method yields results that are independent of the order in which the ligaments are cut, and therefore all ligaments can be studied in each knee. The purpose of this report is to describe how we applied this method to the measurement of the passive restraints to straight medial and lateral opening of human 1258 E. S. GROOD, F. R. NOYES, D. L. BUTLER, AND W. J. SUNTAY THE JOURNAL OF BONE AND JOINT SURGERY cadaver knees at 5 and 25 degrees of flexion, two positions that commonly are tested clinically. Our goals were to document what ligaments resist the forces applied by the clinician when he or she examines the knee for straight medial and lateral laxity; to measure the joint motions that actually occur during the examination; and to determine the biomechanical interactions of the ligaments as they function as stabilizers of the joint. Specimens Materials and Methods we measured the restraining action of the ligaments in sixteen knees (eight right and eight left) obtained from eleven cadavera, eighteen to fifty-five years old (mean age, 36.8 years). Two were female and nine, male. The causes of death included drug overdose, gunshot wound, acute myocardial infarct, stroke, automobile accident, and (in two cadavera that provided three knees) leukemia and septicemia. Only the medial restraints were determined in three knees and only the lateral restraints, in three. In the remaining ten knees, both medial and lateral restraints were measured. Prior to testing, all knees were placed in plastic bags and frozen at -30 degrees Celsius except for one which was tested in a fresh state. The night before testing, the specimens were placed in a refrigerator to thaw at 4 degrees Celsius. Final dissection of the specimens and their preparation before testing were carried out as previously described’.

Comparison of material properties in fascicle-bone units from human patellar tendon and knee ligaments

The fascicle material properties in bone-fascicle-bone units were determined for the anterior and posterior cruciate ligaments (ACL, PCL), the lateral collateral ligament (LCL) and the patellar tendon (PT) from three young human donor knees. Groups of fascicles from each tissue were isolated with intact bone ends and failed at a high strain rate in a saline bath at 37 degrees C. In each knee tested the load related material properties (linear modulus, maximum stress and energy density to maximum stress) for the patellar tendon were significantly larger than corresponding values for the cruciate and collateral ligaments. Bundles from different ligaments in the same knee were similar to each other in their mechanical behavior. In addition, no significant differences were present in the maximum strains recorded for any of the four tissue types examined. The results presented have implications in studies of ligament injury. They are also important in the design and use of synthetic and biological ligament replacements and in tissue and whole knee modeling.

Repair of patellar tendon injuries using a cell–collagen composite

Collagen gels were seeded with rabbit bone marrow‐derived mesenchymal stem cells (MSCs) and contracted onto sutures at initial cell densities of 1, 4, and 8 million cells/ml. These MSC–collagen composites were then implanted into full thickness, full length, central defects created in the patellar tendons of the animals providing the cells. These autologous repairs were compared to natural repair of identical defects on the contralateral side. Biomechanical, histological, and morphometric analyses were performed on both repair tissue types at 6, 12, and 26 weeks after surgery. Repair tissues containing the MSC–collagen composites showed significantly higher maximum stresses and moduli than natural repair tissues at 12 and 26 weeks postsurgery. However, no significant differences were observed in any dimensional or mechanical properties of the repair tissues across seeding densities at each evaluation time. By 26 weeks, the repairs grafted with MSC–collagen composites were one‐fourth of the maximum stress of the normal central portion of the patellar tendon with bone ends. The modulus and maximum stress of the repair tissues grafted with MSC–collagen composites increased at significantly faster rates than did natural repairs over time. Unexpectedly, 28% of the MSC–collagen grafted tendons formed bone in the regenerating repair site. Except for increased repair tissue volume, no significant differences in cellular organization or histological appearance were observed between the natural repairs and MSC–collagen grafted repairs. Overall, these results show that surgically implanting tissue engineered MSC–collagen composites significantly improves the biomechanical properties of tendon repair tissues, although greater MSC concentrations produced no additional significant histological or biomechanical improvement.

Biomechanics of the knee-extension exercise. Effect of cutting the anterior cruciate ligament.

UNLABELLED We conducted this study to determine the effective moment arm of the knee extensor mechanism and the conditions under which the anterior cruciate ligament is loaded during knee-extension exercises. The moment arm was calculated from measurement of the quadriceps force required to extend the knee with and without resistive weights placed at the foot, the leg weight, and the location of its center of gravity. Changes in three-dimensional joint motion after the anterior cruciate ligament was removed were considered to be an indication that the ligament was loaded. The quadriceps force rose during the initial phase of knee extension and remained nearly constant at an average value of 177 newtons between 50 and 15 degrees. With extension past 15 degrees it rose rapidly, reaching an average of 350 newtons at zero degrees of extension, and continued to increase with hyperextension. The addition of thirty-one newtons (seven pounds) at the foot approximately doubled the quadriceps force that was required to extend the knee. The effective moment arm of the extensor mechanism increased with knee extension, peaked at approximately 20 degrees, and rapidly decreased with further extension. No change was found in the quadriceps force or its effective moment arm when the anterior cruciate ligament was sectioned except in hyperextension, where the quadriceps force decreased in two of five specimens. There was, however, an increased anterior tibial displacement in the range of 30 degrees to full extension, suggesting that the anterior cruciate ligament is loaded in that flexion arc. CLINICAL RELEVANCE This study demonstrates that very large quadriceps forces are required to accomplish the last 15 degrees of extension during leg-raising exercises, typically twice those required to reach 30 degrees of flexion. The large forces that are required to obtain full extension explain why an extensor lag occurs with quadriceps weakness even though a full passive range of motion is possible. Since thirty-one newtons (seven pounds) of resistive weight added at the foot approximately doubles the quadriceps forces required to extend the leg alone, using such weights can produce very large quadriceps forces and concurrent patellofemoral and tibiofemoral contact forces. Because the quadriceps force increases little as the leg is extended from 50 to 15 degrees, in patients with patellofemoral chondroses for whom a full range of joint motion is not desired, quadriceps exercises can be limited to the amount of extension without decreasing quadriceps force.(ABSTRACT TRUNCATED AT 400 WORDS)

Knee rehabilitation after anterior cruciate ligament reconstruction and repair

The purpose of this paper is to present the specifics and rationale of our postoperative rehabilitation pro gram after anterior cruciate ligament (ACL) recon struction and compare it with an international survey of 50 knee experts. It is important to stress that what we present is opinion. This opinion, however, is based on principles, guidelines, and specifics which we be lieve are important. The early phases of our program are based upon time and control of forces, both of which are neces sary for ligament healing. The classic parameters of return to play do not indicate healing of ligament tissue and must not be substituted for time restraints. After ACL repair and reconstruction, there are five phases of rehabilitation: maximum protection (12 weeks), moderate protection (24 weeks), minimum protection (48 weeks), return to activity (60 weeks), and activity and maintenance. The maximum protection phase consists of the early healing period and controlled motion period. The early healing period is governed by a principle which re quires the absolute control of forces to prevent dis ruption of the suture line or attachment site. This time will vary according to the surgical technique. We do not allow motion during this period. During the con trolled motion period, we allow motion but control external forces to protect ligament healing. The moderate protection phase consists of the crutch-weaning and walking periods. The major goal of the moderate protection phase is to prepare the patient for walking. The principles which govern Phase 2 are that walking activities create large anterior cru ciate ligament forces and healing strength is still low. A balance of quadriceps and hamstring forces is nec essary for proper knee kinematics. De-emphasis of quadriceps exercises and emphasis of hamstring mus cles is appropriate; however, both muscle groups must be strengthened. The crutch-weaning period is designed to allow the gradual increase of motion and strength to sustain walking activities. A paradox of exercise exists for strength building. To push weight from 30° of flexion into full extension will protect the patellofemoral joint but will create large forces on the ACL. Our compromise is to push low weight through a full range of motion. We begin full weightbearing no sooner than the 16th week. The final three phases of our program are designed to develop dynamic stability through strength, coor dination, and endurance. Phase 3, the maximum pro tection phase, consists of the protected activity period from the 24th through the 36th week, and the light activity period from the 37th through the 48th week. Restrictions include no running, no jumping, and the use of a brace full-time. The light activity period allows further time to protect the slow healer. This may be shortened or lengthened, depending upon the pa tients condition and goals. Phase 4, the return to activity phase, begins 9 to 12 months after surgery. It consists of the advanced rehabilitation period and the running period. The ad vanced rehabilitation period is designed to achieve maximum strength and further enhance neuromuscu lar coordination and endurance. The running period begins when the operated leg has at least 75% of the strength and power of the normal leg. The activity and maintenance phase consists of the return to sport and maintenance periods. On return to sport, the patient must gradually resume full activity by advancing from skill drills. The maintenance pro gram consists of triweekly strength-building sessions, brace protection during sporting, and avoidance of high-risk activities.

In vitro characterization of mesenchymal stem cell-seeded collagen scaffolds for tendon repair: effects of initial seeding density on contraction kinetics.

Mesenchymal stem cells (MSCs) were isolated from bone marrow, culture-expanded, and then seeded at 1, 4, and 8 million cells/mL onto collagen gel constructs designed to augment tendon repair in vivo. To investigate the effects of seeding density on the contraction kinetics and cellular morphology, the contraction of the cell/collagen constructs was monitored over time up to 72 h in culture conditions. Constructs seeded at 4 and 8 million cells/mL showed no significant differences in their gross appearance and dimensions throughout the contraction process. By contrast, constructs seeded at 1 million cells/mL initially contracted more slowly and their diameters at 72 h were 62 to 73% larger than those seeded at higher densities. During contraction, MSCs reoriented and elongated significantly with time. Implants prepared at higher seeding densities showed more well aligned and elongated cell nuclei after 72 h of contraction. Changes in nuclear morphology of the MSCs in response to physical constraints provided by the contracted collagen fibrils may trigger differentiation pathways toward the fibroblastic lineage and influence the cell synthetic activity. Controlling the contraction and organization of the cells and matrix will be critical for successfully creating tissue engineered grafts.

Intra-articular cruciate reconstruction. I: Perspectives on graft strength, vascularization, and immediate motion after replacement.

All of the factors discussed here hopefully will increase the success rate of future intra-articular grafts. But it should not be supposed that the ideal ACL substitution answer is immediately forthcoming. Past experience points to the inherent difficulty of any potential solution and the need to progress in a rigorous scientific manner in the evaluation of the next wave of ligament substitutes. This article reports the utilization of an immediate protective motion program to avoid the problems of postoperative stiffness and lack of knee extension. It can not be stated with certainly whether the same program can be applied to free grafts or to those obtained from other sites. However, the avoidance of these problems will significantly lessen the morbidity of intra-articular reconstruction. The utilization of a vascularized patellar tendon hopefully will add another dimension to ACL replacement.

Functional tissue engineering: the role of biomechanics in articular cartilage repair.

Articular cartilage shows little or no intrinsic capacity for repair in response to injury or disease, and even minor lesions or injuries may lead to progressive damage and joint degeneration. Tissue engineering is a relatively new but rapidly growing field that has sought to use combinations of implanted cells, biomaterials, and biologically active molecules to repair or regenerate injured or diseased tissues. Despite many advances, tissue engineers have faced significant challenges in repairing or replacing tissues that serve a predominantly biomechanical function, such as articular cartilage. An evolving discipline termed functional tissue engineering seeks to address these challenges by emphasizing and evaluating the role of biomechanical factors in the intrinsic and engineered repair of tissues and organs. In the current study, the authors describe some of the fundamental issues involving the interaction of biomechanical stresses in vivo and in vitro with native and repair articular cartilage and with other biomechanically functional tissues. A more thorough and formal investigation of these issues may provide a basis for developing rational design principles for tissue engineered replacement or repair of load-bearing structures in the body.