Acid ceramidase treatment enhances the outcome of autologous chondrocyte implantation in a rat osteochondral defect model.

OBJECTIVE: The overall aim of this study was to evaluate how supplementation of chondrocyte media with recombinant acid ceramidase (rhAC) influenced cartilage repair in a rat osteochondral defect model. METHODS: Primary chondrocytes were grown as monolayers in polystyrene culture dishes with and without rhAC (added once at the time of cell plating) for 7 days, and then seeded onto Bio-Gide® collagen scaffolds and grown for an additional 3 days. The scaffolds were then introduced into osteochondral defects created in Sprague-Dawley rat trochlea by a microdrilling procedure. Analysis was performed 6 weeks post-surgery macroscopically, by micro-CT, histologically, and by immunohistochemistry. RESULTS: Treatment with rhAC led to increased cell numbers and glycosaminoglycan (GAG) production (∼2 and 3-fold, respectively) following 7 days of expansion in vitro. Gene expression of collagen 2, aggrecan and Sox-9 also was significantly elevated. After seeding onto Bio-Gide®, more rhAC treated cells were evident within 4 h. At 6 weeks post-surgery, defects containing rhAC-treated cells exhibited more soft tissue formation at the articular surface, as evidenced by microCT, as well as histological evidence of enhanced cartilage repair. Notably, collagen 2 immunostaining revealed greater surface expression in animals receiving rhAC treated cells as well. Collagen 10 staining was not enhanced. CONCLUSION: The results further demonstrate the positive effects of rhAC treatment on chondrocyte growth and phenotype in vitro, and reveal for the first time the in vivo effects of the treated cells on cartilage repair.

Men and women have similar Q angles: a clinical and trigonometric evaluation.

The Q angle is an important determinant of patellar tracking, though its clinical relevance is debatable. One controversy centres around any possible differences in its value between men and women. The accepted, though unproven explanation, for the greater Q angle in women is that a woman has a wider pelvis. However, because of the long distance between the pelvis and patella, relative to the distance from the patella to the tibial tuberosity, large changes in the position of the anterior superior iliac spine are necessary to effect significant changes in the Q angle. In our study of 69 subjects, we did not find such large differences in the position of the anterior superior iliac spine, and found a mean difference of only 2.3 degrees between the Q angles of men and women. Furthermore, we found that men and women of equal height demonstrated similar Q angles, with taller people having slightly smaller Q angles. The slight difference in Q angles between men and women can be explained by the fact that men tend to be taller.

Applied biomechanics of the patella.

Although numerous prominent orthopaedists of the twentieth century considered the patella to be useless, even detrimental, it now is clear that the patella serves an important biomechanical function. It is a complex lever that magnifies the moment arm of the extensor mechanism. The patellofemoral contact area (the fulcrum of the lever) shifts along a proximodistal axis through the knee's arc of motion. As the knee flexes, the force within the patellar tendon diminishes relative to that of the quadriceps tendon. One's interpretation of patellar tracking is dependent on the choice of coordinates. When assessing tracking by way of anatomic coordinates, patellas are seen to be slightly lateralized at 0 degrees flexion and to follow similar paths down the trochlea. The tracking pattern is the result of an elaborate interplay between the quadriceps muscles, patellofemoral ligaments, the geometry of the trochlea, and the quadriceps angle. The articular cartilage of the patella is the thickest in the human body and does not follow the contour of the subchondral bone. Patellar cartilage is softer and more permeable than that of the trochlea. It is insensate. In size, nature, and number, the facets of the patellar articulation vary from person to person.

Patellofemoral stresses during open and closed kinetic chain exercises. An analysis using computer simulation.

Rehabilitation of the symptomatic patellofemoral joint aims to strengthen the quadriceps muscles while limiting stresses on the articular cartilage. Some investigators have advocated closed kinetic chain exercises, such as squats, because open kinetic chain exercises, such as leg extensions, have been suspected of placing supraphysiologic stresses on patellofemoral cartilage. We performed computer simulations on geometric data from five cadaveric knees to compare three types of open kinetic chain leg extension exercises (no external load on the ankle, 25-N ankle load, and 100-N ankle load) with closed kinetic chain knee-bend exercises in the range of 20 degrees to 90 degrees of flexion. The exercises were compared in terms of the quadriceps muscle forces, patellofemoral joint contact forces and stresses, and "benefit indices" (the ratio of the quadriceps muscle force to the contact stress). The study revealed that, throughout the entire flexion range, the open kinetic chain stresses were not supraphysiologic nor significantly higher than the closed kinetic chain exercise stresses. These findings are important for patients who have undergone an operation and may feel too unstable on their feet to do closed chain kinetic chain exercises. Open kinetic chain exercises at low flexion angles are also recommended for patients whose proximal patellar lesions preclude loading the patellofemoral joint in deeper flexion.

Hamstrings and iliotibial band forces affect knee kinematics and contact pattern.

Many clinical studies have emphasized the role of the hamstrings and the iliotibial band on knee mechanics, although few biomechanical studies have investigated it. This study therefore examined two hypotheses: (a) with loading of the hamstrings, the tibia translates posteriorly and rotates externally and the tibial contact pattern shifts anteriorly; furthermore, the changes in tibial kinematics alter patellar kinematics and contact; and (b) loading the iliotibial band alters the kinematics and contact pattern of the tibiofemoral joint similarly to loading the hamstrings, and loading the iliotibial band laterally translates the patella and its contact location. Five cadaveric knee specimens were tested with a specially designed knee-joint testing machine in an open-chain configuration. At various flexion angles, the knees were tested always with a quadriceps force but with and without a hamstrings force and with and without an iliotibial band force. The results support the first hypothesis. Hence, the hamstrings may be important anterior and rotational stabilizers of the tibia, a role similar to that of the anterior cruciate ligament. The results also support the second hypothesis, although the iliotibial band force had a smaller effect on the tibia than did the hamstrings force. Both forces also changed patellar kinematics and contact, demonstrating that these structures should also be considered during the clinical management of patellar disorders.

The biomechanics of the patellofemoral joint.

Physical therapy for patella malalignment differs from therapy for other knee conditions. In fact, accepted forms of knee therapy can be counterproductive when one is dealing with patella malalignment. This article reviews some of the biomechanical foundations of patella-specific therapy and addresses common controversies. We emphasize the concept of articular cartilage stress over that of joint reaction force. The rationale for strengthening the vastus medialis obliquus and for avoiding certain forms of open chain strengthening are discussed, and we outline some of the exciting work being done in our laboratory concerning patellofemoral tracking, contact area, and cartilage properties.

Patellar stabilization: a quantitative evaluation of the vastus medialis obliquus muscle.

Twenty-one cadaveric knees were dissected to analyze the functional anatomy of the vastus medialis complex (VMC), which is composed of the vastus medialis obliquus (VMO) and the vastus medialis longus (VML) muscles. The physiologic cross-sectional area of the VMO for 20 of the knees was 29% of the total physiologic cross-sectional area for the VMC. These values differed in one knee with a dysplastic VMO. The quantitative description of the VMO provided by this study will facilitate future efforts to accurately model the physiologic function of the VMO in cadaveric investigations on patellofemoral mechanics. The effect of simulated pathologies and surgical reconstructions then may be determined with more certainty to improve patient management.

The medial-lateral position of the patella on routine magnetic resonance imaging: when is normal not normal?

The purpose of this study was to determine the position of the normal patella during routine magnetice resonance imaging (MRI). The literature indicates that the normal patella is positioned laterally relative to the trochlea when the knee is fully extended. As such, a laterally positioned patella on MRI is often interpreted as normal. Yet, in our experience, patients with a normal extensor mechanism show a patella that is centered over the trochlea on MRI, and we set out to formally study this. The MRIs of 60 patients without knee extensor pathology were analyzed. In 59 patients, the patella was centered over the underlying femur. The discrepancy between these results and those in the literature can probably be accounted for by the following: (1) Knees in general are somewhat flexed during MRI, and (2) relative to patients in other studies, patients in this study were subject to stricter criteria of normality. The results of this study strongly suggest that the normal patella is centered over the underlying trochlea during routine MRI. A laterally positioned patella, although possibly common, should not be automatically dismissed as a (medically) normal finding.

Anatomy of the human patellofemoral joint articular cartilage: surface curvature analysis.

Articular cartilage surfaces of 49 human patellae and 24 distal femora were characterized by identifying distinctive features with surface curvature analysis. Paired specimens from the same donor generally exhibited natural symmetry, so only results from nonpaired specimens were considered (39 patellae and 19 femora). In 23 of 39 patellae, proximal median and lateral transverse ridges extended to form an oblique ridge resembling a skewed lambda (lambda). Most of the unpaired patellae (37 of 39) exhibited only a single lateral transverse ridge, and most (32 of 39) had an odd facet. All but one patella exhibited a concave depression in the lateral and medial facets and a sellar area in the proximal region. All distal femoral surfaces exhibited a sellar trochlea. The concavity of the trochlea was greatest in the posterior aspect, near the intercondylar notch.

Osteochondritis dissecans of the distal femur and patella.

Osteochondritis dissecans (OCD) is a pathologic process characterized by a partial or total separation of a fragment of bone with overlying articular cartilage. OCD may affect any joint, but the knee joint is affected most commonly. This article reviews several potential causes of OCD and classification systems for OCD. Diagnosis and treatment strategies are discussed.

Finite deformation biphasic material properties of bovine articular cartilage from confined compression experiments.

In 1990, Holmes and Mow [Journal of Biomechanics 23, 1145-1156] developed a hyperelastic biphasic theory to describe finite deformation behaviors of articular cartilage. To date, however, no experimental finite deformation studies have been made to assess the ability of this constitutive model to describe its finite deformation behaviors (e.g. kinetic creep and stress-relaxation, and equilibrium responses). The objectives of this study are: (1) to investigate whether this hyperelastic biphasic theory can be used to curve-fit the finite deformation compressive stress-relaxation behavior of the tissue, and from this procedure, to calculate its material coefficients; and (2) to investigate whether the theory, together with the calculated material coefficients, can accurately predict the outcome of an independent creep experiment followed by cyclical loading of the tissue. To achieve these objectives, circular cylindrical cartilage plugs were tested in confined compression in both stress-relaxation and creep experiments. Results demonstrated that curve-fits of the stress-relaxation experiments produced nonlinear generalized correlation coefficients of r2 = 0.99 +/- 0.02 (mean +/- standard deviation); theoretical predictions of the creep test differed on average by 10.0% +/- 2.0% relative to experimental results. When curve-fitting the creep experiments as well, it was found that the permeability coefficients differed from those obtained from the stress-relaxation experiments (k0,cr = 2.2 +/- 0.8 x 10(-15) m4 N-1 s-1 and Mcr = 0.4 +/- 0.8 vs k0,sr = 2.7 +/- 1.5 x 10(-15) m4 N-1 s-1, and Msr = 2.2 +/- 1.0); these differences may be attributed to imprecisions in the curve-fitting procedure stemming from the low sensitivity of the stress-relaxation and creep behaviors to large variations of M in the permeability function. Advantages and limitations of this theoretical model are presented in the text.

Unicompartmental knee arthroplasty surgery. 10-year minimum follow-up period.

Sixty knees in 54 patients were followed a minimum of 10 years after unicompartmental knee arthroplasty surgery. Follow-up periods ranged from 10 to 18 years (average, 12 years). In all cases, a Marmor prosthesis was used. Two patients required arthroplasty surgery after the 10-year mark. Seven knees required revision prior to 10 years, and the 10- to 12-year survivorship for the entire cohort was 93%. Slight undercorrection of varus alignment and adequate polyethylene thickness of the tibial component appear to be important contributors to a successful outcome.