Session VI - Geriatrics

Fixation of Distal Femoral Fractures above Total Knee Arthroplasty Utilizing the Less Invasive Surgical Stabilization (L.I.S.S.) System

Philip James Kregor, MD; Peter A. Cole, MD; James L. Hughes, MD, University of Mississippi Medical Center, Jackson, MS

Purpose: The Less Invasive Stabilization System (L.I.S.S.) is currently in clinical trials for treatment of distal femur fractures above total knee arthroplasty. Its characteristics include an outrigger device that allows percutaneous placement of self-drilling cortical-shaft screws, locked fixed-angle screws both proximally and distally, the ability for submuscular fixator placement, and percutaneous proximal screw placement. A prospective clinical review of patients with distal femur fractures above total knee arthroplasty treated with the L.I.S.S. was performed to define the efficacy, indications, advantages, disadvantages, and complications associated with its use.

Methods: A prospective database was established for review of patients treated with the L.I.S.S. for distal femur fractures above total knee arthroplasty. At a university trauma center, from April 1997 until February 2000, all patients with supracondylar femur fracture above a total knee arthroplasty were treated with the L.I.S.S. Patient demographics, fracture characteristics, surgical technique, and patient follow-up are being documented in an ongoing study. Thirteen fractures in 11 patients with an average follow-up of 9 months (4-16 months) have been studied.

The surgical technique is based on a small (approximately 5 cm) incision over the lateral aspect of the femur, closed manipulation of the metaphyseal/diaphyseal component of the fracture, submuscular sliding of the L.I.S.S. fixator without disturbance of the metaphyseal/diaphyseal soft-tissue fracture environment, and percutaneous proximal shaft screw placement. No bone grafting or open visualization of the fracture is performed. No postoperative braces are used, and immediate range-of-motion exercises are begun postoperatively.

Results: Thirteen fractures in 11 patients (11 female) above total knee arthroplasty were treated with the L.I.S.S. Nine patients had isolated injuries. The average age of the patients was 75 years (range, 58-84). All patients had significant medical co-morbidities, including 4 patients with severe dementia. The mechanism of injury was a fall in 10 patients, and a motor vehicle collision in one patient. All fractures were closed, except in one patient with bilateral Type II open fractures. Primary fixation within 24 hours of the injury was performed in 3 patients, and provisional stabilization with splinting or spanning external fixation was performed in the other 8 patients. Ten 13-hole,2 9-hole, and 1 5-hole fixators, with 5-7 proximal screws, and 6-7 distal screws were used. Average surgical time was 140 minutes, and average time for placement of the L.I.S.S. fixator was 70 minutes. Intra-operative complications included one broken K-wire. Postoperative reductions revealed a 5-degree excess valgus deformity in one case, and one case of 8 mm of anterior translation of the proximal femoral shaft.

All fractures healed without need of additional surgeries or modalities. Eventual range-of-motion averaged 2 degrees (range 0-5) of extension, and 90 degrees (range 40-115) of flexion. No cases of varus collapse and/or distal femoral condyle screw loosening was seen. No infections were noted.

Discussion: Nonoperative treatment of supracondylar femur fractures is associated with inability to maintain fracture reduction, skin breakdown, nonunion, and loss of joint motion. Surgical treatment of the fractures above total knee arthroplasty remains a significant surgical challenge, with high complication rates. Adverse events include infection, decreased range-of-motion, failure of fixation, need for bone grafting, malunion, and nonunion. Emphasis on preservation of osseous vascularity using indirect reduction techniques in the supracondylar femur has led to increased rates of union without bone grafting.(1) Recent advances in submuscular plate applications using existing plate constructs appear to offer considerable advantages, especially with regard to lowering the rate of infection and the need for bone grafting.(2)

A particular clinical problem in these fractures is loss of fixation of the distal femoral fragment, especially in osteoporotic bone and/or with use of the condylar buttress plate. Loss of distal fixation and/or toggling of distal screws can lead to varus angulation and/or fracture fixation failure, either when using plate or intramedullary nail constructs. Different modalities have been used to combat fixation failure in the distal femoral fragment. Recently, the L.I.S.S. internal fixation system has been developed to provide multiple, fixed-angle locked screws; it can be best thought of as an "internal" external fixator.

Significant and early callus formation was observed in the fractures analyzed. All fractures healed without bone grafting or use of postoperative bracing. Postoperative reduction quality was acceptable and may be improved with further refinement of closed reduction techniques and/or reduction aids. Of particular note, no loss of fixation in the distal femoral condyles was observed.

Conclusion: L.I.S.S. stabilization of distal femoral fractures above total knee arthroplasty using closed reduction techniques for the shaft component is associated with acceptable union rates and eventual range-of-motion. Advantages appear to include high union rates without bone grafting (100%), low rate of infection (0%), and maintenance of distal femoral fixation (100%) in a population characterized by osteoporotic patients. Disadvantages may include difficulties with closed reduction techniques.

References:

1. Bolhofner BR, et al. J Orthop Trauma 10:372-7, 1996.

2. Krettek C, et al. Injury Supplement (I): 20-30, 1997.