Abstract
Correct alignment of tibial and femoral components is one of the most important factors that determine favorable long-term results of total knee arthroplasty (TKA). Computer-assisted TKA allows for more accurate component positioning and continuous intraoperative monitoring of the alignment. However, the pinholes created by the temporally anchored pins used as reference points may cause problems. Here we report a case of tibial stress fracture that occurred after a TKA was performed with the use of a computer navigation system.
Case report
The patient, a 76-year-old woman (height 157 cm, weight 73 kg and BMI 29.5 kg/m2) with bilateral knee osteoarthritis. The right knee was replaced first and recovered without complications. The left knee was replaced 2 weeks later. The patient underwent computer-assisted (Stryker Co., Allendale, NJ, USA), cemented, posterior cruciate ligament sacrificing replacement of the left knee (with a Zimmer Gender Solutions Knee). A midline skin incision was made and a 5.0 mm bicortical self-tapping anchoring pin was inserted 10 cm below the tibiofemoral joint line. The other anchoring pin was inserted into the femur at the same distance from the joint to the line. These pins were inserted bicortically, anterior to posterior. Femur and tibia resections were performed according to the light-emitting diode tracker on the navigation system and cutting jig. Femoral and tibial implants were fixed with cement. The anchoring screws were then removed after the fixation of all implants.
For two weeks, the patient tolerated significant walking but experienced only vague pain and swelling at the site of the left proximal tibial area. Local heat or redness was not observed and inflammatory serological markers (erythrocyte sedimentation rate, c-reactive protein level and white blood cell count) were within normal limits. One week later the patient complained of more aggravated and persistent pain. The patient immediately had a radiography check-up which showed a long linear radiolucent line and cortical defect through the pinholes (Fig. 1A–D). Through close scrutiny of the radiographs taken immediately after and two weeks after the operation, it was realized that she had a tibial stress fracture resulting from a misplaced fixation pin (Fig. 2A, B). As a result, the patient wore a long leg splint and was instructed to avoid weight bearing for two weeks. She was then allowed to gradually put more weight after wearing along leg cast for four weeks. Clinically, a satisfactory outcome was reported by the patient with good recovery of her daily activities; crutches were no longer needed to walk after three months. Physical examination showed no tenderness and final ROM was 0–120 degrees. Radiography showed that the stress fracture was completely healed (Fig. 3A, B).
Conclusively, we suggest that unicortical anchoring pins with a small diameter should be considered for use in the metaphyseal area and avoidance of transcortical drilling is recommended. Care should be taken to avoid stress fracture during rehabilitation in case of the development of pain after a pain-free period following computer assisted TKA.
