Mid‐head Resection of Hip using Resurfacing Prosthesis

Introduction

Birmingham hip resurfacing (BHR) and other prosthesis have been used clinically since the 1990s and have produced good outcomes, particularly for hip osteoarthritis, osteonecrosis of the femoral head (ONFH), Developmental dysplasia of the hip, and rheumatoid arthritis and ankylosing spondylitis that have caused osteoarthritis1, 2, 3. Compared with the conventional total hip arthroplasty, these procedures permit a better range of motion, stability and ease of sequent revision surgery and decrease bone loss. Thus young subjects with high demands for quality of life particularly benefit from such procedures. However, in patients with large necrosis, femoral head deformity or heavy femoral head cysts, the residual bone is barely sufficient to support the prosthesis. McMinn designed the Birmingham mid‐head resection (BMHR) prosthesis, in which the prosthesis fixed in the head–neck transition zone. Because the BMHR belongs to the the same family of implants as BHR, surgeons can initiate the procedure with the same bone cuts and then perform either a BHR or BMHR depending on the quality of bone discovered introperatively4, 5, 6, 7, 8.

Case Presentation and Surgical Technique

With the patient supported in the lateral position and the pubis and sacrum fixed, the patient's pelvis is fixed in a neutral position. Using a modified posterolateral incision as recommended by McMinn, a point 5 cm inferior to the tip of the trochanter is marked along the posterior border of the trochanter, and a 12 to 15 cm incision is marked from this point posterosuperiorly at an angle of about 25° to the long axis of the femoral shaft. The skin, subcutaneous tissue and fascia are then routinely separated. Using blunt dissection or electrocautery the gluteus maximus is divided along the line of its fibers and the piriformis, piriformis tendon, short external rotators and part of the quadratus femoris are severed near the piriformis fossa. The posterior capsule is then incised and the femoral head dislocated from the acetabulum by flexion and internal rotation, after which the inferior aspect of the anterior hip capsule is incised. Flexing and forcibly internally rotating the hip allows sufficient exposure to continue the procedure. If osteophytes are present, they are excised from the femoral head, taking care not to tear the soft tissue off the femoral head. The neck and head dimensions are then measured and the minimum femoral head components are confirmed. The next task is to place a guide wire using the correct guide‐wire positioning. Once the guide wire has gone down the center of the femoral head, the drilling hole can be enlarged. The guide bar having been positioned correctly, the femoral head is barrel file polished. The BMHR femoral osteotomy guide ring is then installed according to the line marked for resection of the proximal femoral head and sectioned with a file. A change to a short guide rod is then made, the BMHR handle type selected and the head and neck transition region shaped with the same type of taper reamer. The next step is to place the hip in extension and insert a Hohmann retractor between the calcaneum and acetabulum. To completely expose the acetabulum, the femur must be distracted anteriorly. The lip of the acetabulum is resected using an acetabulum file to mill down to fresh bleeding subchondral bone. A matching acetabular prosthesis is chosen and the prosthesis kept in an abduction of 40° and 20° forward position. The implant is then stabilized with pressure. The femoral side is then exposed again, after cystic lesions scraped and is implanted autogenous bone grafted to implant the BMHR short shaft, after the femoral head prosthesis is implanted with pressure. Finally, the hip joint is reduced and joint activity and stability tests are performed.

Discussion

Indications

The indications for BMHR include not only joint osteoarthritis, osteonecrosis of the femoral head, acetabular dysplasia and rheumatoid arthritis and ankylosing spondylitis that have caused osteoarthritis, but also advanced ONFH, femoral head deformity and heavy femoral head cysts that cannot be adequately managed using BHR. This procedure is suitable for young people who below to years of age and have larger activity. The correct procedure can be determined intraoperatively according to the location of lesion; if the area of necrosis extends 5 cm above the head–neck transition area, this prosthesis can be implanted stability. Particular attention should be paid to patients in whom the neck diameter is less than 40 cm because they are at increased risk of femoral neck fracture. Additionally, women of child‐bearing age and patients with metal sensitivity or renal disease should not receive metal‐to‐metal prosthesis because of the associated metal‐ion complications9, 10, 11.

Incision and Exposure

In conventional total hip arthroplasty, the femoral head is exposed by the incision provided the hip is dislocated and the tibia vertical. However, in this position hip resurfacing arthroplasty cannot be performed. Some surgeons have tried to divide the gluteus maximus more proximally; however, this has proved to be a poor approach because of the risk of damages of the superior gluteal vessels and nerve bundles directly and the main nerve that innervates the gluteus maximus muscle. Others have tried to leverage the femoral head from anteriorly, which failed for disturbing the blood supply and aggravating the ONFH. It is preferable to have the assistant internally rotate the hip and completely expose the lesion superiorly, allowing the surgeon to incise the anterior capsule from inferiorly using Muller scissors after having sighted the anterior capsule and confirmed the upper edge of the psoas tendon. Actually, the key to the BMHR procedure is to expose the femoral head completely and allow it to protrude. For the learner surgeon, larger incisions are acceptable if necessary.

Femoral Neck Central Position Technique

The femoral neck central position technique is very important. It is important to locate the center of the femoral neck rather than femoral head. The guide pin and shaft should be at a 135° to 140° angle, which is somewhat larger than the neck‐shaft angle. What's more, the guide pin should be inserted as closely parallel as possible to the medial margin of the femoral neck. The key to correct placement of the center positioning pin is to have good exposure of the surgical field, especially of the femoral neck. Removal of osteophytes and cleaning of the residual synovial tissue around the neck are important12. Revealing the true form of the femoral neck, including its anterior, posterior and lateral aspects, and protecting the blood supply are two additional keys. As to the importance of the central position technique, any bias should be corrected as soon as possible and without hesitation.

Postoperative Rehabilitation

The BMHR is a biological type of fixed prosthesis with good stability. On the first postoperative day, the patients can be provided with a half sitting table and perform exercises, including flexing the contralateral hip and lifting the hip manually to prevent pressure sores. In addition, the operation side limb should not be adducted or internally rotated across the midline of the body within 6 weeks of surgery, nor should the hip be in more than 90° of flexion. Exercise is important for facilitating venous return and pulmonary inflation. On the second postoperative day, the drainage tube can be removed and the patient allowed out of bed with crutches. On the third postoperative day, the patients can get in and out of bed without assistance and on the fourth day, be taught to go up and down stairs. The patient can be discharged from hospital on the sixth postoperative day and return to work within 6 weeks to 2 months.

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Supporting information

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