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Total Hip Arthroplasty: First Experiences with Pinless THA Software to Determine Leg Length and Offset
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Abstract
A rigid body fixation on the proximal femur is required for navigation during total hip arthroplasty. In surgery requiring a small incision, the fixation mechanism (C clamp or screw) may cause soft tissue damage and may force enlargement of the approach. New software available for the OrthoPilot navigation system (B. Braun Aesculap, Tuttlingen, Germany) eliminates the need for a rigid body at the femur. Only one rigid body is placed on the iliac crest. Two additional palpations, one at the greater trochanter and one at the patella, establish the system of coordinates between pelvis and femur so that leg length and offset changes can be indicated.
Two reference points between the pelvis and the femur are required for total hip arthroplasty (THA) when using the OrthoPilot navigation system (B. Braun Aesculap, Tuttlingen, Germany), one at the iliac crest and one at the proximal femur. C clamp fixation is typically used at the femur and at cup navigation.1,2 This reference point may block the surgical field. During stem preparation and navigation, the C clamp may increase soft tissue tension and might induce soft tissue damage. To prevent this damage, the surgeon may choose to enlarge the incision, resulting in an approach that is up to 3 cm larger than the standard incision without navigation.3 The C clamp fixation may be even more problematic in minimally invasive surgery with an anterolateral or a direct anterior approach.4
A new software system (THAplus) for OrthoPilot (B. Braun Aesculap) has been developed to assist surgeons with stem insertion during THA. During navigation with THAplus software, no rigid-body fixation on the femur is needed. The femoral registration is performed with two pointers that can be used in a minimally invasive approach without damaging the soft tissue. First experiences with this new navigation system are described in this study.
Materials and Methods
A lateral approach THA in the supine position under general anesthesia was performed on 25 patients between June 2006 and December 2006. An entry incision, averaging 10 cm, was made one-third distal and two-thirds proximal to the tip of the trochanter. After splitting the fascia lata, the aponeurisis of the vastus lateralis and the gluteus medius muscle were dissected from the greater trochanter. The rectus femoris and the iliacus muscle were separated from the anterior acetabulum rim under flexion to prevent damaging the femoral nerve, and a tipped Hohmann retractor was placed directly on the rim and the anterior capsule of the hip resected (Figure 1).
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Figure 1: Lateral approach THA in the supine position. | |
After a stitch incision was made, a rigid body was placed on the ipsilateral iliac crest. With a pointer, the anterior pelvic plane is registered. For the initial determination of leg length and offset, a point at the lateral greater trochanter was marked.
Using a sterile pen, a second mark was made on the skin in the center of the patella while the knee was in 90° of flexion. The trochanter mark and the patella mark were registered with two pointers simultaneously. Care must be taken during the palpation of these marks because they must be located again during the preparation of the stem.
These points are referenced to the rigid body on the iliac crest and must be registered while the knee is in 90° of flexion (Figure 1).
After luxation of the hip, resection of the femoral neck, and removal of the femoral head, a second tipped retractor was placed at the posterior rim of the acetabulum. Preparation and navigation of the cup were performed, and a cup implant (B. Braun Aesculap) was placed under navigation control with the OrthoPilot.1 Following the cup implantation, the stem preparation was begun in external rotation with the knee in 90° of flexion. With the osteoprofiler in place, the position of the stem could be controlled. The reference frame was then placed on the handle of the osteoprofiler. The two previously marked reference points at the trochanter and the patella were reregistered, and changes in leg length and offset indicated on the computer screen (Figure 2). After registration, operative parameters, such as head diameter and implant type, can be changed and the results simulated. After placing the stem implant, the final position can be accomplished in the same manner.
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Figure 2: Screen shots of OrthoPilot for offset and leg length changes. |
Results
From June 2006 to December 2006, 25 endoprothesis were implanted using the new software THAplus with OrthoPilot. In all cases, a Plasmacup NSC and Bicontact S stem (B. Braun Aesculap, Germany, Tuttlingen) were used. All procedures were performed by a single surgeon. The average duration of the operation was 60 minutes. Registration and simulation of the stem position were easily carried out and without complications in all cases.
Preoperative leg length was clinically and radiologically registered. Intraoperative change in leg length and offset were registered and confirmed with a C arm. Postoperatively, all parameters were checked clinically and radiologically. Changes in leg length and offset were indicated properly and reproducible in all cases.
Discussion
The new software THAplus for OrthoPilot indicates cup position and changes in leg length and offset. The elimination of a rigid body intraoperatively makes the use of small incisions possible. This software may be useful to determine the leg length and offset changes without enlarging the approach for navigation tools, such as C clamps or other fixation devices, especially during implantation of short-stem prosthesis and when using a direct anterior approach. Compared with full stem navigation with femoral rigid body fixation, however, limited information on the stem position is delivered.1 The workflow is very easy to perform. Screens for the stem navigation are clearly arranged, and the possibility of simulating different stem, cone, and head combinations are highly sophisticated and useful.
References
- Walde HJ, Walde TA. First results in navigated total hip arthroplasty. Orthopedics. 2006; 29(10 suppl):S139-S141.
- Kiefer H, Othman A. OrthoPilot total hip arthroplasty workflow and surgery. Orthopedics. 2005; 28(10 suppl): S1221-S1226.
- Kiefer H. OrthoPilot cup navigation-how to optimize cup positioning? Int Orthop. 2003; 27 (suppl 1):S37-S42.
- Lazovic D, Kaib N. Results with navigated bicontact total hip arthroplasty. Orthopedics. 2005; 28(10 suppl):S1227-S1233.
Authors
Dr Schmerwitz is from the Department of Orthopaedic and Trauma Surgery, Lukas Krankenhaus, Hindenburgstraße.
Correspondence should be addressed to: u.schmerwitz@lukas-krankenhaus.de
Dr Schmerwitz has received financial compensation from B. Braun Aesculap.