Presented at NACOB 98: North American Congress on Biomechanics Canadian Society for Biomechanics - American Society of Biomechanics University of Waterloo Waterloo, Ontario, Canada August 14-18, 1998

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THE EFFECTS OF CHANGING THE FEMORAL COMPONENT POSITIONS
IN TOTAL KNEE ARTHROPLASTY

S.M. HAN ¹ , I. ZIV ^2
1 School of Mechanical Engineering, Pusan National University, Pusan City, Korea
² Departments of Orthopaedic Surgery and University at Buffalo, Buffalo, NY

INTRODUCTION

This study examines the changes in posterior cruciate ligament (PCL) strain, patellar tendon (PT) strain, and PT force created by altering the femoral component position in total knee arthroplasty (TKA).

REVIEW AND THEORY

Decreased range of motion (ROM) is a common problem after total knee arthroplasty. Some researchers1,2 have reported on posterior cruciate ligament and patellar tendon strain related to TKA. However, none have investigated the effect of femoral component position on ligament strain as it relates to ROM. The purpose of this research is to determine the effects of changing the femoral component position on strain and load in the PCL and PT, and knee ROM.

PROCEDURES

PCL and PT strain and PT force were measured from 30 to 120o of flexion on ten fresh cadaveric legs. Strain and force were measured before and after TKA using differential variable reluctance transducers and a force probe with a quadriceps load of 22N and 89N. Six different femoral component positions were studied using 4mm spacers: 1. Anterior reduction (A-4, mm) 2. Anatomical (A0) 3. Anterior augmentation (A+4) 4. Distal augmentation (D4) (Figure 1) 5. Anterior and Distal augmentation (A4D4) 6. Posterior augmentation (P4).

The femur was horizontal during testing to eliminate effects of gravity

Figure 1. Distal augmentation of the femoral component

RESULTS

PCL strain increased with flexion and quadriceps load for each component position, ranging between 11-27.9% at 120° (Table 1). Position A-4 had the lowest PCL strain after TKA.

Table 1. Ligament strain and force averages at 120° flexion with 89N for the seven testing conditions (n=10).

The increase in PCL strain was greater for A+4, A4D4, and P4 than that recorded for A0 and D4. PT strain ranged from 1-9% and was greater for A+4, D4, A4D4 and P4 at 120o flexion. PT force averaged from 180 to 312N and was largest for A+4.

DISCUSSION

Anterior reduction of the femoral compoent results in decreased strain in the PCL. Correcting the anterior reduction has little effect on PCL strain. Distal augmentation can lead to large increases in PCL strain at high degrees of flexion. Posterior augmentation led to overall decreased strain when compared to template matched TKA. Increasing loads cause very minor changes in PT strain. Anterior reduction and postrior augmentation configuration had the highest PT force generation. The effect of thicker tibial components on the PCL has been reported1,2. This study has demonstrated that removing too little anterior or distal femoral bone during TKA increases strains and force in the PCL and PT, which may lead to a decreased knee flexion.

REFERENCES

1. Incavaco, SJ, et al: Clinical Orthopaedics Related Research, 1994.

2. Mahoney, OM, et al: J. Arthroplasty, 1994.