Subtrochanteric fractures after internal fixation of femoral neck fractures are rare but severe complications. Hansson Pinloc system (Pinloc) consists of three pins locking into a plate (Fig. 1). In biomechanical trials, the novel plate design with its pin configuration enhanced torsional stability ^[1]. Pinloc has been used for femoral neck fracture in some countries including Sweden and Japan. Recently, the outcome of a randomized clinical study comparing Pinloc and conventional Hansson pins was published ^[2]. However, subtrochanteric fracture after internal fixation using Pinloc has not been reported in the English literature including the above report. Only several Japanese literatures reported some cases with this post-operative complication. We present a case with subtrochanteric fracture after internal fixation using Pinloc.

A 67-year-old woman (164 cm, 40.4 kg) fell while walking and injured her right hip. She visited our hospital on the same day. The first X-ray showed a Garden stage I fracture in the right femoral neck (Fig. 2).

Osteosynthesis was performed with Pinloc 3 days after she sustained the injury (Fig. 3). She was discharged 3 weeks after surgery, walking with a cane. One week after discharge, she developed sudden severe pain in the right hip on standing up. She was unable to walk and was transferred to our hospital by ambulance. The X-ray revealed a fresh subtrochanteric fracture in the femur (Fig. 4). We performed a second surgery as described below on the 3^rd day after this subtrochanteric fracture was sustained (Fig. 5).

Findings at the second surgery

The patient was placed in supine position on the traction table, and the displacement of fracture site was examined using an image intensifier. Displacement was mild on the frontal view, but the proximal fragment was extremely displaced anteriorly on the lateral view. We attempted closed reduction but could not achieve satisfactory reduction. The skin incision was elongated to expose the fracture site better. We then lifted the distal fragment and reduced anatomically under direct view. After open reduction, we fixed the fragments with a wire temporarily. Then, after the hook on the upper rear side pin of the Pinloc was withdrawn, we tried to remove the pin using the T-handle, as instructed by the manufacturer. At that point, a new fracture occurred at the distal end of the fragment. All three hooks were withdrawn back into the pins and the plate was pulled out with all of the pins as one unit. There was a bony defect in the femoral neck and head after removal of the implant. This was filled with hydroxyapatite bone cement (Lagfix; Stryker, Kalamazoo, MI). We made another skin incision over the greater trochanter and inserted an intramedullary nail (T2 reconstruction nail; Stryker). The hip screws were driven into the proximal fragment, avoiding the bony defect site.

Post-operative course

After non-weight-bearing for 3 weeks, we allowed the patient to bear weight as tolerable. She could walk with double crutches by 9 weeks after surgery and was discharged home. X-ray at the last follow-up showed no migration or loosening of the implant at 2 months after the second surgery (Fig. 6).

Internal fixation for femoral neck fracture is commonly performed using the cannulated cancellous hip system or Hansson Pinloc System. The rates of subtrochanteric fracture after osteosynthesis with these systems have been reported to be 1–3% [3, 4, 5, 6, 7]. Risk factors for subtrochanteric fracture after surgery have been reported, as follows [4, 8, 9, 10, 11]: (1) Screws or pins inserted below the lesser trochanter; (2) screws or pins positioned too close to each other; (3) three screws that form a pyramid, with the apex directed proximally; (4) reinsertion of the guide wire more than once; and (5) the patient has osteoporosis. We considered each of these risk factors for trochanteric fracture as it related to our case. Post-operative X-ray revealed that the distal pin had been inserted above the distal end of the lesser trochanter. Based on the structure of the Pinloc, all three pins had not been positioned too close to each other, and they did not form a pyramid with the apex directed proximally. Furthermore, the guide pin was not reinserted more than once. In terms of osteoporosis, a dual-energy X-ray absorptiometry scan had given a T score of −4.1 in the lumbar spine and −3.0 in the femur. The patient thus had severe osteoporosis but had not yet been treated. There was, therefore, a possibility that bone fragility due to severe osteoporosis had caused the subtrochanteric fracture after surgery. Kalland et al. reported on outcomes of osteosynthesis using Pinloc in a prospective control study and stated that the three pins connected to the lateral plate of Pinloc may exert increased stress on the subtrochanteric region, leading to a higher rate of subtrochanteric fracture ^[2]. They showed that three new fractures occurred in 169 cases treated with Pinloc but did not clarify whether these were subtrochanteric or other fractures. Furthermore, in a retrospective study on 40 patients treated with Pinloc, no subtrochanteric fracture was reported ^[12]. To the best of our knowledge, there are no reports in the English literature on this complication. The Japanese literature has five reports on subtrochanteric fracture after osteosynthesis using Pinloc [11, 12, 13, 14, 15]. In these cases, all the patients were women, and re-fracture occurred within 1 month after surgery; three patients had subtrochanteric fracture with no preceding episode of trauma (Table 1).

Urata et al. reported that subtrochanteric fracture with no preceding trauma occurred in one of 18 patients who had internal fixation with Pinloc ^[11]. They cautioned that there is a higher risk of subtrochanteric fracture with Pinloc compared with other implants. In our case, the patient had subtrochanteric fracture with no trauma. Therefore, attention should be paid to the probability of this fracture as a post-operative complication when using Pinloc in patients with osteoporosis. Only one report has described a method to avoid this complication; Isozumi et al. proposed downsizing the diameter of the guide pin from 3.2 mm (the size of a Pinloc pin) to 2.4 mm (the size of a conventional Hansson pin) ^[12]. We discuss the treatment strategy for subtrochanteric fracture after osteosynthesis for femoral neck fracture. Several reports have described various osteosynthesis implants such as compression hip screw, Ender nail, bipolar hemiarthroplasty, and intramedullary nail. In our case, the second surgery had been performed 4 weeks after the initial procedure for femoral neck fracture. Therefore, we assumed that bone healing was incomplete, and proceeded with internal fixation using an intramedullary nail, which could fix both the femoral neck and the subtrochanteric fracture. At the second surgery, a new fracture occurred when we attempted to remove the Pinloc. To prevent this complication in other cases, we recommend that surgeons first withdraw all three hooks in the pins, and then pull out all three pins with the plate as one unit. Furthermore, any bony defect after removing the Pinloc should be adequately addressed. Tani et al. reported that the bony defect occupied about 25% of a femoral neck cross-section on computed tomography, so the defect needed to be refilled. In our case, we filled the bony defect with artificial bone ^[13].

Surgeons should be cognizant of this post-operative complication before using Pinloc. Future studies are needed to clarify the frequency of subtrochanteric fracture after internal fixation using this system. In osteosynthesis of the femoral neck fracture using Pinloc, we should keep in mind that subtrochanteric fracture is a possible post-operative complication.

Subtrochanteric fractures after internal fixation of femoral neck fractures are rare but severe complications. Pinloc is new device, in which improved torsional stability though it may stress on the subtrochanteric region. In osteosynthesis of the femoral neck fracture using Pinloc, we should keep in mind that subtrochanteric fracture is a possible post-operative complication.