Incredible position of broken sliding dynamic hip screw implant in the medial of thigh.

We report a case with implant failure after nailing of an unstable pertrochanteric fracture with dynamic hip screw. The patient presented with a medial sided thigh pain at 5 years after the surgery. Plain radiographs showed nonunion of the fracture with distant migration of assembled hip screw and side plate to the subcutaneous area of the inner thigh.

Introduction

Intertrochanteric fracture is the most common osteoporotic fracture in the elderly especially in women. Dynamic hip screw (DHS) implant system is one of the devices used for fixation of intertrochanteric fractures. Failure of DHS has been reported multiple times in different parts of the implant,3, 4, 5, 6 but to the best of our knowledge, a side plate with assembled sliding hip screw, all as one piece, placed to the medial of thigh following device failure with broken screws has not been reported yet.

Case report

An 84-year-old woman came with pain and mass on medial aspect of left thigh. She had undergone reduction and fixation of left pertrochanteric fracture with DHS implant via direct lateral approach about five years before presentation (Fig. 1, Fig. 2). She could walk with a cane without any pain in left hip area. In exam, a strange bulging was palpable in subcutaneous area of medial left thigh. All nerves beside vascular supply of the left lower limb were intact. Although she had osteoarthritis of the knee joint with decreased range of motion of the knee joint, motion of joints of left lower limb was equal to the right side. Moreover no evidence of infection in exam and laboratory data was detected.

Fig. 1

Pre-op anteroposterior plain radiograph showed unstable pertrochanteric fracture.

Fig. 2

Post-op anteroposterior plain radiograph displayed reduction and fixation with DHS implant.

On the plane anteroposterior radiograph, nonunion and deformed pertrochanteric area beside migrated implant in an unbelievable position of medial thigh was obvious (Fig. 3). The broken implant and engaged screws were simply removed through medial thigh incision exactly on the prominent device (Fig. 4). The patient denied any surgery to correct nonunion because of painless walking using a cane.

Fig. 3

Anteroposterior plain radiograph of the patient revealed nonunion and incredible position of broken device in medial of thigh.

Fig. 4

Sequences of implant removal during surgery (A to E).

One year after removal of the implant on medial side of the thigh, the patient was pain free but dependent on a cane for walking.

Discussion

As stated by Spivak et al there are two modes of failure of DHS implant; the usual kind is the result of multiple-cycle, low stress fatigue failure of the device which is related to the design of screw such as its internal threaded region and barrel length. The other type of DHS failure is the result of high stress loading which is seen in nonunion of pertrochanteric area. The presented subject was a case of unstable subtrochanteric-intertrochanteric femoral fracture of left side. The mechanical stability of DHS to achieve union in this case was inadequate; therefore implant failure was clear from beginning. Another cause of failure in this case would be occult infection which was ruled out by exam and normal laboratory data.

Technical malposition of hip screw may result in immediate failure of the implant. This common failure of the implant is called “cut out” which is penetration of the screw to the hip joint with varus deformity in the site of fracture. Cut out of the implant from the femoral neck is seen in about 7% of patients treated with DHS implant. Accurate position of the screw in the femoral neck, considered as tip-apex distance, is the most useful criterion to prevent sliding screw cut out. Other factors including unstable pattern of fracture, inadequate reduction of the fracture, trabecular bone strength, and age of the patient were determined as the other predictive factors.7, 8, 9

Beside cut out of the hip screw from femoral neck to the hip joint, several types of failure in hip screw have been reported in the literature such as bending of the hip screw at the screw–barrel interface without breakage, hip screw breakage,10, 11 and breakage in the barrel of plate and bending in the hip screw. Breakage of side plate or cortical screws especially in nonunion cases have been described previously but migration of unbroken hip screw linked to the side plate into the medial side of the thigh has not been reported.

In conclusion, fixation of unstable pertrochanteric fractures with DHS may result in nonunion and eventually device failure and displacement with possible injuries to the surrounding vital structures.