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Instruments aid accuracy of THR done through 5-cm incision

The system is universal and permits precise bone cuts and component alignment.

Issue: Issue 2 2003

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NEW ORLEANS — Developers of a keyhole total hip replacement procedure said the minimally invasive technique ensures accurate component positioning and permits patients to rehabilitate quickly.

Since the hip is not dislocated during surgery, ligaments and muscles are minimally disturbed and morbidity is reduced, according to the developers, who have used it to treat 58 patients.

--- During tissue tensioning, the "lollipop" device may be used in conjuction with two spacers, as shown here. The spacers correspond to medium and long neck lengths.
COURTESY OF EUGENE SHERRY

The technique is indicated for primary total hip replacement (THR) in patients with osteoarthritis, rheumatoid arthritis or osteonecrosis. It is contraindicated in obese patients when a posterolateral approach is contraindicated, or where there is severe deformity of the femoral head or neck.

Use of this THR technique is still in the early stages — the longest follow-up is 18 months — but average Harris Hip Scores of 30 preoperatively increased to 87 postoperatively, the Australian developers said.

Great expectations

Because the early results are promising and since most hip surgeons can readily learn the technique — usually after about four hours of training and performing five cases — developers are optimistic about how the technique may change the way THR is performed in the future.

--- The system’s cutting block was designed to cut the femoral neck without dislocating the hip at the procedure’s start.
COURTESY OF EUGENE SHERRY

The technique is performed using a patented navigationless instrument system called the NILNAV Hip System. Most patients only require a single 5- to 7-cm posterolateral incision behind the greater trochanter, but overweight patients may require a 10-cm incision. “In 10% of cases, I extend the incision 2 to 4 cm. The instruments also allow you to do a much more accurate operation no matter what the length of the incision,” according to Eugene Sherry, MD, FRACS, of Sydney Private Hospital. He developed the system with engineer Michael Egan.

Sherry presented preliminary results using the system in a poster presentation during the 70th Annual Meeting of the American Academy of Orthopaedic Surgeons in New Orleans.

Universal system

The developers are hoping orthopaedic surgeons worldwide will accept the NILNAV Hip System because it is universal. It works with several manufdsacturers’ models of cemented or cementless hip prostheses. Sherry has used the NILNAV system for THR using cementless as well as cemented stems and cups, such as Link’s uncemented C.F.P stem and pressfit T.O.P. acetabular cup and Howmedica’s ABG hip.

--- An A-frame is shown holding the lollipop device in place. The lollipop has a drop alignment guide to indicate the correct position of the acetabular cup, which is attached to it prior to impaction.

The technique does not require intraoperative imaging or a surgical navigation system. Instead, a precision tool kit allows the surgeon to exactly locate the femoral neck and then cut it using a cutting block. A jig system ensures accurate orientation of the acetabular cup in relationship to the stem. “Before, this was always done in an arbitrary manner. Now the cup can only be placed in one position,” Sherry said. Proper cup orientation typically reduces component dislocation, maltracking and long-term wear. Part of the jig system is an alignment device called a lollipop, which is held perpendicular to the table. The acetabular cup is attached to the lollipop and then impacted in the proper position.

Soft tissue tensioning is practically foolproof by adding up to two spacers to the lollipop, which “allow the right soft tissue tension to be determined and [provide] a final check of the orientation of the cup relative to the stem,” he said. Spacers also help the surgeon avoid doing multiple trial reductions.

The technique is much less invasive, Sherry said, as cone dissection is 96% less than is typically necessary with traditional THR procedures. Because it produces less pain, a smaller scar and faster rehabilitation, patients prefer this surgery, he added. On average, patients are discharged from the hospital two days after surgery, and most require just two postoperative physical therapy sessions. “I recently did a 98-year-old man who was walking the next day,” he told Orthopaedics Today.

At least 20 orthopaedic surgeons from Australia, New Zealand, Malaysia and the United States are currently being trained to perform the technique.

For your information:

• Sherry E, Sivananthan DKS, Sivananthan S, et al. Minimal invasive surgery for hip replacement using the NILNAV Hip System. Poster #512. Presented at the 70th Annual Meeting of the American Academy of Orthopaedic Surgeons. Feb. 5-9, 2003. New Orleans.
• Sherry E, Egan M, Henderson A, Warnke PH. Minimal invasive hip replacement using the SE Hip System. Presented at the 62nd Annual Scientific Meeting of the Australian Orthopaedic Association. Oct. 13-18, 2002. Melbourne.