Richard D. Komistek

Femoral condylar lift-off in vivo in total knee arthroplasty.

We carried out weight-bearing video radiological studies on 40 patients with a total knee arthroplasty (TKA), to determine the presence and magnitude of femoral condylar lift-off. Half (20) had posterior-cruciate-retaining (PCR) and half (20) posterior-cruciate-substituting (PS) prostheses. The selected patients had successful arthroplasties with no pain or instability. Each carried out successive weight-bearing knee bends to maximum flexion, and the radiological video tapes were analysed using an interactive model-fitting technique. Femoral lift-off was seen at some increment of knee flexion in 75% of patients (PCR TKA 70%; PS TKA 80%). The mean values for lift-off were 1.2 mm with a PCR TKA and 1.4 mm with a PS TKA. Lift-off occurred mostly laterally with the PCR TKA, and both medially and laterally with the PS TKA. Separation between the femoral condyles and the articular surface of the tibia was recorded at 0 degrees, 30 degrees, 60 degrees and 90 degrees of flexion. Femoral condylar lift-off may contribute to eccentric polyethylene wear, particularly in designs of TKA which have flatter condyles. Coronal conformity is an important consideration in the design of a TKA.

“In vivo” determination of hip joint separation and the forces generated due to impact loading conditions

Numerous supporting structures assist in the retention of the femoral head within the acetabulum of the normal hip joint including the capsule, labrum, and ligament of the femoral head (LHF). During total hip arthroplasty (THA), the LHF is often disrupted or degenerative and is surgically removed. In addition, a portion of the remaining supporting structures is transected or resected to facilitate surgical exposure. The present study analyzes the effects of LHF absence and surgical dissection in THA patients. Twenty subjects (5 normal hip joints, 10 nonconstrained THA, and 5 constrained THA) were evaluated using fluoroscopy while performing active hip abduction. All THA subjects were considered clinically successful. Fluoroscopic videos of the normal hips were analyzed using digitization, while those with THA were assessed using a computerized interactive model-fitting technique. The distance between the femoral head and acetabulum was measured to determine if femoral head separation occurred. Error analysis revealed measurements to be accurate within 0.75mm. No separation was observed in normal hips or those subjects implanted with constrained THA, while all 10 (100%) with unconstrained THA demonstrated femoral head separation, averaging 3.3mm (range 1.9-5.2mm). This study has shown that separation of the prosthetic femoral head from the acetabular component can occur. The normal hip joint has surrounding capsuloligamentous structures and a ligament attaching the femoral head to the acetabulum. We hypothesize that these soft tissue supports create a passive, resistant force at the hip, preventing femoral head separation. The absence of these supporting structures after THA may allow increased hip joint forces, which may play a role in premature polyethylene wear or prosthetic loosening.

An in vivo analysis of the effectiveness of the osteoarthritic knee brace during heel-strike of gait

The objective of this study was to analyze the effects of off-loading knee braces in patients diagnosed with symptomatic unicompartmental osteoarthritis. Under fluoroscopic surveillance, 15 patients were asked to perform normal gait on a treadmill. Each patient was asked initially to walk without using a knee brace and then to walk while wearing a brace. The fluoroscopic images of the patients at heel-strike were downloaded to a workstation computer. Condylar separation angle of the knee joint and the distances from the medial and lateral femoral condyles to the tibial plateau (condylar separation) were measured. Twelve of 15 patients (80%) reported relief of pain and demonstrated condylar separation of the degenerative compartment with the use of the off-loading brace. The 3 patients who did not demonstrate condylar separation were obese, making accurate brace fitting difficult. The average change in condylar separation and condylar separation angle was 1.2 mm (range, 0.0-4.5 mm) and 2.2 degrees (range, 0.0 degrees-7.8 degrees). This study demonstrated that condylar separation of a degenerative knee compartment can be achieved with off-loading braces with subsequent subjective relief of knee pain.

An in vivo determination of patellofemoral contact positions.

OBJECTIVE To determine patellofemoral contact patterns in two-dimensions for normal and implanted patients. DESIGN An in vivo, weightbearing fluoroscopy analysis of 14 subjects with normal knees, 12 with anterior cruciate ligament deficient knees, 14 with a posterior cruciate retaining implant, and 25 with a posterior cruciate substituting implant. BACKGROUND Most previous experimental studies involving the knee joint have been either in vitro or under nonweightbearing conditions. METHODS Subjects were studied under fluoroscopic surveillance performing deep knee bends to maximum flexion. Video images were analyzed on a computer with a two-dimensional technique of digitizing discrete points on the patella, femur, and tibia. RESULTS The contact position, measured from the patella mass center, was inferior on the patella at extension and moved superior during flexion. Average contact positions of the implanted knee groups were more superior than the normal knee group throughout the flexion cycle. Analysis of patellar tilt angle demonstrated a flexed posture of the patella relative to the tibia. Increase in patellar tilt angle with increasing femorotibial flexion was substantially greater in implanted knees versus normal knees. Separation of the patella from the femur in full extension was absent in normal knees, but present in 86% and 44% of posterior cruciate retaining and posterior cruciate substituting total knee arthroplasties, respectively. CONCLUSIONS The patellofemoral kinematics of the total knee arthroplasties analyzed in the study was statistically different than the normal and anterior cruciate ligament-deficient knees. The kinematic variations observed between normal and implanted knees may be related to disturbed femorotibial kinematics previously observed to occur following total knee arthroplasty. RELEVANCE Patellofemoral complications, including polyethylene wear, are a major concern in total knee arthroplasty. Since the causes of polyethylene wear are multi-factorial, abnormal patellofemoral kinematics may play a role in patellar failure.

A determination of ankle kinematics using fluoroscopy.

In vivo weight-bearing studies utilizing dynamic video fluoroscopy have been shown to offer an accurate and reproducible method for determining the kinematics of a joint. The purpose of this study was to evaluate translational and rotational motions of the distal tibia relative to the talus in the sagittal and frontal planes. Ten subjects, each having a normal ankle and a total ankle arthroplasty on the opposite side (Buechel-Pappas Total Ankle, Endotec, South Orange, NJ), were studied under in vivo, weight-bearing conditions using video fluoroscopy. All ten subjects were judged to have a successful arthroplasty without demonstrable pain or ligament instability. Under weight-bearing conditions, each subject performed successive motions moving from maximum dorsiflexion to plantarflexion. At maximum dorsiflexion, both the normal and implanted ankles had similar sagittal midline talar contact positions but with plantar flexion, implanted ankles had increased posterior talar contact. Contact points on the distal tibia revealed that the lateral surface contacted at the midline or posterior throughout range-of-motion with minimal translation. The medial distal tibia contacted the talus posterior on plantarflexion and often moved anteriorly with dorsiflexion. This translation described relative external rotation of the distal tibia on plantar flexion and internal rotation on dorsiflexion. The measured distances were larger for the implanted ankles with higher variability. The average range-of-motion was 37.4° for normal ankles and 32.3° for implanted ankles. This study defines the normal kinematic rotational and translational motions of the ankle joint by accurately describing the three dimensional joint orientations. The implanted ankles experienced rotational and translational motions but had contacts more posterior, possibly related to surgical technique or alterations of ligamentous tension.

In vivo kinematics and kinetics of the normal and implanted TMJ

INTRODUCTION: The objective of this present study is to assess the in viva kinematics and kinetics of the temporomandibular joint (TMJ). METHODS: Fifteen subjects (5 normal, 5 metal-on-metal implants, 5 fossa-only implants) were evaluated using fluoroscopic videos (TMJ Implants, Denver, CO). Under fluoroscopic surveillance, the subjects were asked to onen and close their iaw on a force transducer olaced between their molars &rest the joint (