Outcome of Open Reduction and Internal Fixation With Cannulated Cancellous Screw and Washer in Avulsion Fracture of the Posterior Cruciate Ligament Tibial Attachment: A Descriptive Observational Follow-Up Study

Background: Avulsion of the tibial insertion of the posterior cruciate ligament (PCL) is an uncommon but functionallyimportant injury. A displaced bony avulsion left unreduced leaves the knee posteriorly unstable and predisposes topatellofemoral and medial compartment degeneration. Open reduction and internal fixation (ORIF) with a cannulatedcancellous (CC) screw is widely used, but reported series are small and the influence of the interval between injury and surgeryon outcome has received little attention. Materials and Methods: Thirty-five skeletally mature patients with an isolated,displaced (> 3 mm) PCL tibial avulsion fracture with a fragment larger than 20 mm were treated by ORIF through a modifiedBurks and Schaffer posterior approach using a 4 mm partially threaded CC screw with a washer. Patients were reviewedclinically and radiologically at 2, 4, 6 and 12 weeks and at 6 months. Outcome measures were time to radiological union, kneerange of motion, the Lysholm knee score, wound-related problems and other complications. Continuous variables are reportedas mean ± standard deviation; paired scores were compared with the Wilcoxon signed-rank test and group differences with theMann–Whitney U or Fisher exact test, with p < 0.05 taken as significant. Results: The mean age was 40.6 ± 10.4 years (range24–58); 27 patients (77.1%) were male. A road traffic accident was the mechanism in 22 patients (62.9%). The mean intervalfrom injury to surgery was 18.3 ± 9.3 days (range 2–35). Radiological union was achieved in all 35 knees (100%) at a meanof 11.1 ± 2.3 weeks. The mean Lysholm knee score improved from 3.6 ± 3.6 pre-operatively to 97.4 ± 1.7 at 6 months (p <0.001), an excellent result in every patient, and the mean arc of knee motion was 129.6° ± 3.5°. Wound-related problemsoccurred in 15 patients (42.9%) and other complications — pain in 4 and persistent swelling in 2 — in 6 patients (17.1%);there was no non-union, implant failure or neurovascular injury. A longer injury-to-surgery interval correlated with slowerunion (Spearman ρ = 0.72, p < 0.001) and, compared with patients operated within 14 days, patients operated later united moreslowly (12.1 ± 2.3 vs 9.6 ± 1.2 weeks, p = 0.003), regained less motion (128.5° ± 3.3° vs 131.3° ± 3.1°, p = 0.023) and hadmore wound problems (61.9% vs 14.3%, p = 0.007), although the final Lysholm score did not differ (p = 0.42). Conclusion:ORIF with a single 4 mm partially threaded cannulated cancellous screw and washer through a posterior approach gives reliableunion and an excellent functional result in displaced PCL tibial avulsion fractures. Delay to surgery did not compromise thefinal Lysholm score but was associated with slower union, a smaller arc of motion and a markedly higher rate of woundproblems, which argues for early fixation once the soft tissues permit.