Original Research

Biomechanical Analysis of a Novel Buried Fixation Technique Using Headless Compression Screws for the Treatment of Patella Fractures

Publish date: July 10, 2018

References

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Patella fractures are common injuries that can cause considerable disability to the knee extensor apparatus.^1-3 Transverse patella fractures are the most common fracture pattern associated with patella fractures.{Harrell, 2003 #3}² Given that the patella plays a crucial role in knee extensor biomechanics, its proper integrity is vital for physiological knee motion and ambulation.⁴ Traditionally, patella fractures with >2 mm of displacement have been managed with cannulated screws or Kirschner wires (K-wires) and a stainless-steel wire tension band.^5-9 The goal in the treatment of patellar fractures is to reduce fracture fragments accurately and to minimize additional insults to the articular cartilage.¹⁰

Despite advances in surgical protocols and acceptable radiographic outcomes, functional impairment remains common after the treatment of patella fractures. Functional impairment includes knee pain, screw head pain, implant removal, wire breakage, and patella baja.¹ The need for implant removal is one of the most common complications following the open reduction internal fixation of patella fractures.^2,11 The subcutaneous and exposed nature of the patella in conjunction with soft tissue irritation resulting from standard fixation (SF) predisposes the patient toward prominence and discomfort with the retained implant. Although nonunion rates are low, the rate of implant removal can reach as high as 52%.^2,10-12 To overcome some of these complications, we designed a novel buried fixation (BF) method for the treatment of transverse fractures. Our method minimizes the amount of exposed implant to improve patient comfort and potentially reduce the need for future implant removal. These effects are achieved by using headless compression screws and nonabsorbable sutures to attenuate the soft tissue irritation associated with traditional fixation.¹³ While our novel technique has demonstrated improved clinical results, it has not been tested biomechanically against a traditional fixation technique. Therefore, this study aims to evaluate and compare the structural integrity of our novel BF technique with that of the standard technique that uses cannulated screws and wire tension band. We hypothesized that the stability provided by our technique would be similar to that provided by SF for transverse patella fractures.

MATERIALS AND METHODS

SPECIMEN PREPARATION

Thirteen matched pairs of fresh-frozen human cadaveric knees were obtained from a Cedars-Sinai approved tissue bank. Specimens were cut midfemur and were intact to the foot. Legs with major structural bony or ligamentous abnormalities, extensor mechanism disruption, or septic knees were excluded from testing. To assess the bone quality of each specimen prior to testing, dual-energy X-ray absorptiometry was performed using a GE Lunar iDXA scanner (GE Healthcare). Specimens were stored at −30°C and thawed at room temperature for 24 hours prior to biomechanical testing.

A midline anterior approach to the patella was performed, and the extensor retinaculum, quadriceps tendon, and patellar tendon were exposed. A digital caliper was used to measure the craniocaudal and mediolateral dimensions of the patella, and a transverse osteotomy (Arbeitsgemeinschaft für Osteosynthesefragen/Orthopaedic Trauma Association [AO/OTA] type 34-C1) was created at the midway point between superior and inferior poles by using an oscillating saw. The retinaculum was then incised to the level of the midaxial line of the femur. One leg from each matched pair was allocated to the SF group, and the other was allocated to the BF group. Left and right legs were alternately assigned to each group to ensure that laterality was balanced between the 2 groups.

SURGICAL TECHNIQUE

The repair of the specimens in the SF group involved the use of 2 parallel 4.0-mm partially threaded cannulated screws (Acumed) and an 18-gauge monofilament steel wire (Ethicon) in a figure-eight tension band (Figure 1A). The repair of the specimens in the BF group involved the use of 2 parallel standard Acutrak headless compression screws (Acumed), a No. 2 FiberWire (Arthrex) in a figure-eight tension band, and a No. 5 FiberWire (Arthrex) was applied as cerclage around the patella (Figure 1B).

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Biomechanical Analysis of a Novel Buried Fixation Technique Using Headless Compression Screws for the Treatment of Patella Fractures

References

MATERIALS AND METHODS

SPECIMEN PREPARATION

SURGICAL TECHNIQUE

Pages

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