Case series on the effectiveness of preoperative radiological templating on acetabular cup orientation in total hip arthroplasty of developmental dysplasia of the hip

Neetin P Mahajan; Ajay S Chandanwale; Sangeet K Gawhale; GS Prasanna Kumar; Lalkar Gadod

doi:10.4103/jcrsm.jcrsm_70_20

CASE SERIES

Year : 2021 | Volume : 7 | Issue : 1 | Page : 42-48

Case series on the effectiveness of preoperative radiological templating on acetabular cup orientation in total hip arthroplasty of developmental dysplasia of the hip

Neetin P Mahajan¹, Ajay S Chandanwale², Sangeet K Gawhale¹, GS Prasanna Kumar¹, Lalkar Gadod¹
¹ Department of Orthopaedics, Grant Government Medical College, Mumbai, India
² Joint Director, Directorate of Medical Education and Research (DMER), Mumbai, India

Date of Submission	21-Sep-2020
Date of Decision	31-Oct-2020
Date of Acceptance	02-Feb-2021
Date of Web Publication	02-Jul-2021

Correspondence Address:
G S Prasanna Kumar
Department of Orthopaedics, Grant Government Medical College, Mumbai, Maharashtra
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/jcrsm.jcrsm_70_20

Abstract

Total hip arthroplasty becomes the challenging treatment in cases of neglected developmental dysplasia of the hip but requires elaborate preoperative planning, especially for the restoration of the normal hip center, correction of shortening, and achieve normal biomechanics to avoid limb and early failures. To determine the morphological changes resulting from the dysplasia, the anatomic acetabular position, the height of the femur head dislocation and the combined anteversion must all be established. Preoperative planning was done using 100% zoom digital X-rays of the pelvis with both hips in 15° of internal rotation. This included identification of true acetabulum and centre of hip rotation using Ranawat's triangle. Templating was done to determine the position of acetabulum and size of the cup and required length of subtrochanteric osteotomy. The length of subtrochantric osteotomy was determined so that it would not lengthen the leg more than 3 cm to prevent sciatic nerve stretching. The postoperative X-rays were compared with the template of X-rays for the effectiveness of preoperative planning in restoring the near-normal biomechanics of the hip joint.

Keywords: Acetabular cup, dysplasia of hip, dislocation, templating, total hip replacement

How to cite this article:
Mahajan NP, Chandanwale AS, Gawhale SK, Prasanna Kumar G S, Gadod L. Case series on the effectiveness of preoperative radiological templating on acetabular cup orientation in total hip arthroplasty of developmental dysplasia of the hip. J Curr Res Sci Med 2021;7:42-8

How to cite this URL:
Mahajan NP, Chandanwale AS, Gawhale SK, Prasanna Kumar G S, Gadod L. Case series on the effectiveness of preoperative radiological templating on acetabular cup orientation in total hip arthroplasty of developmental dysplasia of the hip. J Curr Res Sci Med [serial online] 2021 [cited 2023 Mar 24];7:42-8. Available from: https://www.jcrsmed.org/text.asp?2021/7/1/42/320508

Introduction

Developmental dysplasia of the hip (DDH) can be associated with morphological alterations on both the acetabular and the femoral side. Total hip arthroplasty (THA) becomes the challenging treatment in cases of neglected DDH but requires elaborate preoperative planning, especially for the restoration of the normal hip center, stability, correction of shortening, and achieve normal biomechanics to avoid limp and early failures. In recent years, patients have been increasingly expecting the better restoration of functionality after surgery, and the main reason for patient dissatisfaction after the procedure is perceived leg length discrepancy (LLD). Thus, extensive research has been focused on the LLD, in particular for severely dislocated hips. Postoperative LLD can be a consequence of several factors, such as cup position, inequalities in bony structure, pelvic tilt, and a more inferior change in the original acetabulum. Preoperative planning is a challenging and essential process for THA with DDH. All potential morphological changes should be revealed before surgery.

In neglected DDH cases with hip arthritis, THA is an effective treatment option for pain relief and stability, but it requires complex preoperative planning and radiological templating.^[1] A severely dysplastic acetabulum is frequently associated with bone deficiency.^{[1],[2],[3],[4]} Femur has excessive anteversion, narrower intramedullary canal, malformed anatomy of the proximal femur, and abnormal bony length and hypoplastic acetabulum.^[2] The commonest issues encountered during reaming and placement of acetabular cup are segmental deficiencies of walls and secondary shallowness, inadequate depth of true acetabulum, excessive anteversion, abnormal distribution of bone stock mainly located anteroposteriorly in relation to the true acetabulum.

Digital X-rays of pelvis with Both hip – Anteroposterior (AP) view in 15° of internal rotation and 90% zoom X-rays are effective in preoperative planning of neglected DDH. Preoperative planning was done using 100% zoom digital X-rays of the pelvis with both hips in 15° of internal rotation. This included identification of true acetabulum and centre of hip rotation using Ranawat's triangle. Templating was done to determine the position of acetabulum and size of cup and the required length of subtrochanteric osteotomy. The length of subtrochantric osteotomy was determined so that it would not lengthen the leg more than 3 cm to prevent sciatic nerve stretching. The postoperative X-rays were compared with the template of X-rays for the effectiveness of preoperative planning in restoring the near-normal biomechanics of the hip joint.

Following case series have been put forward for assessing the influence of the preoperative conventional radiological templating in reducing intraoperative struggles and postoperative morbidities amongst the patients operated for DDH arthritis.

Case 1

A 45-year-old male presented to us with history of difficulty in walking since childhood and pain in left hip for the last 2 years. On examination, the patient was walking with lurch on the left side due to shortening and abductor lurch. All hip movements were painfully restricted due to hip arthritis. The measured limb length discrepancy was 6 cm shortening.

On radiological examination X-ray pelvis with both hips AP view [Figure 1]a and [Figure 1]b revealed proximally migrated dysplastic head of the femur with the dysplastic shallow empty acetabulum. Acetabular angles on both sides were 60°.

Figure 1: (a) X-ray pelvis with both hips anteroposterior view showing proximally migrated dysplastic head of femur with dysplastic shallow empty acetabulum. Acetabular angles on both sides were 60°. (b) X-ray pelvis both hips showing the preoperative planning with acetabular angle of 60°. (c) Postoperative X-ray pelvis both hips showing the uncemented total hip replacement with subtrochantric osteotomy with head in the true acetabulum. (d) Postoperative X-ray pelvis both hips showing the restoration of normal hip biomechanics

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Preoperative planning included identification of true acetabulum and centre of hip rotation using Ranawat's triangle. The dislocation was Crowe's type IV. Templating was done to determine the position of acetabulum, size of cup and required length of subtrochanteric osteotomy. The length of subtrochantric osteotomy was determined so that it would not lengthen the leg more than 3 cm to prevent sciatic nerve stretching.

All necessary investigations were done and anesthetic clearance was taken. The patient was planned for left-sided uncemented THA in single stages. The patient was positioned in the lateral position. The hip joint was approached by a posterolateral incision over the posterior aspect of greater trochanter curved over the buttock. Exposure in such cases is challenging because of distorted anatomy. Soft tissues were contracted with tight adhesions. It should be kept in mind that femoral neurovascular bundle and sciatic nerve may not be present at usual anatomic positions. True acetabulum was identified by direct palpation and using C-ARM. Acetabulum was cleared of fibrous tissues and progressively large reamers were used to enlarge the shallow acetabulum. Using power reamer it was shaped spherical and a trial implant was used to determine the coverage of the cup. Ischial and pubic bone were exposed proximally along with teardrop to get a clear idea of available bone stock. The medial wall was sufficient to re-shape a proper acetabulum. No structural Bone Grafting was required in Acetabular reconstruction. Size 44 mm pinnacle acetabular cup with marathon poly and solution stem with titanium metal head prosthesis was used. Acetabulum was stable and well seated with coverage of >90%. A subtrochanteric femoral osteotomy of four centimetres was done to facilitate the reduction. To facilitate the reduction the proximal femur was pulled down by thorough soft-tissue release. Capsule and iliopsoas tendon were released and abductors were lengthened by pi-crusting. The prosthetic joint then can be reduced without undue tension. Postoperative X-rays were analysed for the restoration of hip biomechanics. The hip center was located at the normal center of the true acetabulum [Figure 1]c and [Figure 1]d. The neck length was restored. Subtrochanateric osteotomy with 3 cm of resection was performed. The stem was snugly fixed in diaphysis and metaphysis. Level of greater trochanter was equal as compared to the right side. Anteversion was 10° on acetabular side. No excessive uncoverage of the metal head seen.

The patient had uneventful recovery in the post-operative period. Physiotherapy in bed was started the next day after surgery. The patient was mobilised with support 3 weeks after surgery. Full weight-bearing started at 6 weeks. The postoperative limb length discrepancy was 2 cm of shortening at 1 year and lurch was corrected after shoe raise.

Case 2

A 64-year-old Male presented to us with history of difficulty in walking since childhood and pain in both hip for last 1 year. On examination, the patient was walking with waddling gait. All hip movements were painfully restricted due to hip arthritis. The measured limb length discrepancy was 1 cm shortening on the left side.

On radiological examination, X-ray pelvis with both hips AP view [Figure 2]a and [Figure 2]b revealed subluxated enlarged mushroom-shaped dysplastic head of the femur with dysplastic shallow widened acetabulum. Acetabular angles on both sides were <20°. Computed tomography (CT) was done to assess the bone stock.

Figure 2: (a) X-ray pelvis with both hips Anteroposterior view showing subluxated enlarged mushroom shaped dysplastic head of femur with dysplastic shallow widened acetabulum. (b) X-ray pelvis both hips showing preoperative planning. Acetabular angles on both sides were <20°. Computed tomography was done to assess the bone stock. (c) Three dimensional computed tomography pelvis showing dysplastic femur head and the acetabulum. (d) X-ray pelvis both hips showing the uncemented Right sided total hip replacement with reconstruction of acetabular wall using femoral head graft and fixed with screws

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Preoperative planning included identification of true acetabulum and centre of hip rotation using Ranawat's triangle. The dislocation was Crowe's type II. Templating was done to determine position of the acetabular hemisphere, to judge deepening of reaming up to floor to create hemisphere and size of the cup. Reconstruction of the superior deficient wall of acetabulum using head graft for cup coverage superiorly was anticipated preoperatively for management of deficient bone stock as dictated by CT three dimensional (3D) reconstruction images also.

All necessary investigations were done and anesthetic clearance was taken. The patient was planned for right-sided uncemented THA in single stages. Patient was positioned in lateral position. The hip joint was approached by a posterolateral incision over the posterior aspect of greater trochanter curved over the buttock. Soft tissues are contracted with tight adhesions. Acetabulum was identified by direct palpation and using C-ARM. Acetabulum was cleared of fibrous tissues and progressively large reamers were used to enlarge the shallow acetabulum. Reaming was completed till the floor and available depth of the medial wall was identified. Using power reamer, it was shaped spherical and a trial implant was used to determine the coverage of the cup. Ischial and pubic bone were exposed proximally along with teardrop to get a clear idea of available bone stock. The medial wall was reamed deeply sufficient to re-shape a proper Acetabulum. Structural Bone Grafting from the femoral head was required in Acetabular reconstruction. The head graft was reshaped with reamer and fixed at the superior wall defect for coverage of cup. Zimmer triology acetabular system shell Size 62 mm with liner standard longevity cross-linked polyethene 36 mm and 3.5 mm offset prosthesis was used. Acetabulum was stable and well seated with coverage of more than 90%. We used femoral Stem Versys hip system femoral head 12/14 taper 36 mm diameter; 20 mm length. The patient had uneventful recovery in the postoperative period. Physiotherapy in bed was started the next day after surgery. The patient was mobilized with support 4 weeks after surgery. X-rays at 4 months follow-up showed good stable implants with good callus formation at the osteotomy sites. There was no limb length discrepancy in follow-ups [Figure 2]c and [Figure 2]d.

Case 3

A 55-year-old Male presented to us with history of difficulty in walking since childhood and pain in right hip for the last 2 years. On examination, the patient was walking with lurch on the right side due to shortening and abductor lurch. All hip movements were painfully restricted due to hip arthritis. The measured limb length discrepancy was 4 cm shortening.

On radiological examination, X-ray pelvis with both hips, AP view [Figure 3]a and [Figure 3]b revealed proximally migrated dysplastic head of the femur with dysplastic shallow empty acetabulum Crowe's type IV. Preoperative planning included identification of true acetabulum and centre of hip rotation using Ranawats triangle. The hip dislocation was Crowe's type IV. Templating to determine the position of acetabulum and size of cup and required length of subtochanteric osteotomy. The length of subtrochanteric osteotomy was determined so that it would not lengthen the leg more than 3 cm to prevent sciatic nerve stretching.

Figure 3: (a) X-ray pelvis both hips showing proximally migrated dysplastic head of femur with dysplastic shallow empty acetabulum Crowe's type IV. (b) Postoperative X-ray showing right hip uncemented total hip replacement

Click here to view

All necessary investigations were done and anaesthetic clearance was taken. The patient was planned for left-sided Uncemented THA in single stages. Patient was positioned in Lateral position. Hip joint was approached by a posterolateral incision over the posterior aspect of greater trochanter curved over the buttock. Exposure in such cases is challenging because of distorted anatomy. Soft tissues are contracted with tight adhesions.

Using the posterior approach, True acetabulum was identified by direct palpation and using C-ARM. Acetabulum was cleared of fibrous tissues and progressively large reamers were used to enlarge the shallow acetabulum. Using power reamer it was shaped spherical and a trial implant was used to determine the coverage of the cup. Ischial and pubic bone were exposed proximally along with tear drop to get a clear idea of available bone stock. The medial wall was sufficient to re-shape a proper Acetabulum. No structural Bone Grafting was required in Acetabular reconstruction. Size 48 mm Zimmer acetabular cup with marathon poly and ML taper stem with titanium metal head prosthesis was used. Acetabulum was stable and well seated with coverage of more than 90%. To facilitate the reduction the proximal femur was pulled down by thorough soft-tissue release. Capsule and iliopsoas tendon were released and abductors were lengthened by pi crusting. The prosthetic joint then can be reduced without undue tension. Postoperative X-rays were analyzed for the restoration of hip biomechanics. The hip centre was located at the normal centre of true acetabulum. The neck length was restored. C stem was snugly fixed in diaphysis and metaphysis. Level of the greater trochanter was equal as compared to the right side. Anteversion was 10° on acetabular side. No excessive uncoverage of the metal head seen.

The patient had uneventful recovery in the postoperative period. Physiotherapy in bed was started the next day after surgery. The patient was mobilised with support 4 weeks after surgery. X-rays at 4 months follow-up showed good stable implants and there was no limb length discrepancy in follow-ups.

Discussion

The most common anatomical deviations in relation to dysplastic hip are shallow and wide acetabulum having high acetabular index radiologically. Cup coverage and restoration of normal hip biomechanics remain the most important issues. The most common issues encountered during reaming and placement of acetabular cup are segmental deficiencies of the superior wall, secondary shallowness attributable to fossa covering osteophytes or complete absence of superior, anterior and posterior segmental deficiency, narrow opening and inadequate depth of true acetabulum. Segmental deficiency of the entire acetabulum with narrow opening inadequate depth, excessive anteversion, abnormal distribution of bone stock mainly located anteroposteriorly in relation to the true acetabulum. Acetabulum is hypoplastic with narrow femoral medullary canal. A wide range of prostheses acetabular cup designs and augments should be available to choose one which is best suited for hypo plastic bones. The 100% Zoom Digital X-rays on large films offers a good alternative to consider various options from different choices of implants in the armamentarium. It also gives an opportunity to prepare plan for dealing with various anatomical variations and pathologies expected to come in the way of safe surgical procedures. The various intraoperative obstacles are expected to be handled on 2D planning and templating of implants. However, following important considerations are required to be discussed for good acetabular cup placement and longevity of total hip replacement in arthritis of dysplastic hips.

Estimate of acetabular bone stock

AP pelvic radiographs and CT images are used to evaluate the acetabular bone stock, and cup coverage can be estimated on postoperative pelvic radiographs. Some authors demonstrate that 2-dimensional (2D) measurements are not as accurate as 3D^[5],[6],[7] but whether the former overestimates or underestimates cup coverage is controversial^[5],[6] We tend to believe that 2D images overestimate the actual acetabular bone stock, due to the bone shield.

Placement of acetabular Cup

The true position of the acetabulum is easily confirmed using Ranawat's triangle or other methods with AP pelvic radiographs. However, usually, the teardrop on the deformed side in the radiograph is a more convenient marker of the acetabular cup position and is used more frequently in preoperative planning.^[4],[8]

Prediction of prosthesis size

Some authors have compared the accuracy of digital templating in THA between Crowe type II or III hips and hips with other primary diagnoses. In one study, the predicted cup size of the DDH group was not as accurate as that of the control group (48.8% and 73.2%, respectively), while the predicted stem sizes were comparable (70.8% and 79.2%).^[9] CT scan-based 3D templating has also proved an effective method to predict the size of components in THA for hips with dysplasia (estimated in cups and stems as, respectively, 92% and 98%, each within ± one size).^[10] However, in our case series, acetabular cup and femoral stems sizes were accurate for intraoperative placements. It saved unnecessary efforts and loss of available crucial and natural bone stock.

Balance of leg length for severely dislocated hips

One of the most common complications after THA of hips with severe dysplasia is LLD, and LLD is the main reason for patient dissatisfaction after surgery. Liu et al.^[11] notes that for patients with DDH, perceived LLD is a great cause of anxiety and depression, before and after THA. Chen et al.^[12] report that a postoperative LLD of 10 mm or more in patients with DDH would lead to an asymmetric gait. For patients with DDH types Crowe I or II, LLD can be easily corrected. However, the severe deformities of the acetabulum and proximal femur in Crowe III and IV hips makes correcting leg length balance a complicated process, which needs to be decided before surgery.

According to Li et al.,^[13] An anatomical LLD is produced by a different level of dislocation in each leg. A functional LLD is experienced subjectively by the patient while in a standing position. Balancing the leg length for a patient with DDH can be complicated and challenging because of the many factors that can affect the leg length in hip dysplasia, such as the height of dislocation, pelvic tilt, pelvic imbalance, and the height of acetabular components. Corrections must be chosen on a case-by-case basis.

Bearing surface

In the meta-analysis of Lee et al.,^[14] the revision rate for all-reason, aseptic loosening, or periprosthetic joint infection with MoM was higher than that of CoC. This was in accord with the study result of Hu et al.^[15] To our knowledge, CoC bearings have a lower wear rate than do MoP or CoP.^{[16],[17],[18]} Sentuerk et al.^[19] reported that CoC, with the lowest wear rate and ability to control fracture and squeaking risk, should be an excellent choice for the young active patient undergoing THA.

Restriction of surface bearing choices

Acetabulum with dysplasia are always shallow and small, and these deformities will become more severe with the increasing dysplasia level of the hip. Therefore, THA for high dislocated hips can encounter an especially small acetabulum, which makes using normal size cups and heads a challenge. Yet, cups and heads of smaller size will jeopardise hip stability, and limit the polyethene thickness and utility of CoC bearings (which requires a 44-mm minimum cup size). Xu et al.^[20] introduced a method using normal sized cups (≥44 mm) to treat high dislocated hip. In their series 11 of 13 hips were treated with 44-mm cups and the other two hips were treated with 46-mm cups.

Reduction of prosthesis

Anatomical reduction of prosthetic components can be possible only after lengthening of shortened abductors. In this case, we did pie crusting of abductors to gain satisfactory length.

Bone grafting

Structural bone grafting is traditionally done in acetabular reconstruction to reinforce deficient supero-lateral aspect. In this patient, we obtained >90% acetabular cup coverage on both sides. Without structural bone grafting. Shinar and Harris^[21] have reported high failure rates in long term with the use of Structural graft and recommended its use only as a last resort. Acetabular reconstruction has high failure rate if graft covers a large proportion of the cup. Although some authors have reported satisfactory results using structural bone graft^[22],[23] Biant et al.^[24] reported excellent results in Crowe type III and IV dysplastic hips at 10 years follow up using S-ROM stem. 21 of 28 patients in his case series required autologous bone grafting. We think that whenever bone stock permits cementless cup fixed with screws without structural bone grafting, it gives good result.

Conclusions

THA in untreated DDH is a technically demanding procedure and anatomical reconstruction of the hip joint requires experience and technical support to provide pain-free functionally good hip. Preoperative planning is a challenging and essential process for THA with DDH. All potential morphological changes should be revealed before surgery. In most situations, acetabular construction is the gold standard, so the anatomic position of the acetabulum should be confirmed using C Arm whenever required. Whether cup support techniques are needed is decided based on the acetabular bone stock. The height of the dislocation of the femoral head is a key factor to predict leg length after THA and is important for a leg length balance strategy. If the height of dislocation is more than 3.5 cm, osteotomy is considered to help reduce and protect the sciatic nerve. Both acetabular and femur anteversion may be more than the normal range. Controlling a combined anteversion that is <55° is an effective way to avoid dislocation after surgery. For hips with severe morphological changes, CT-based 3D reconstruction would help to analyze acetabular bone stock and other issues of cup coverage. An integrated leg length balance strategy should take into consideration the three types of LLD, pelvic tilt, pelvic imbalance, and cup position. The choice of prosthesis is made after measurement of the combined anteversion and observation of the proximal femur morphology.

Clinical message

Preoperative planning especially radiological templating using 100% zoom X-rays helps to predict acetabular position, proper prosthesis selection and adequate soft-tissue dissection especially tight abductors and flexors. Good radiological planning is the key to success in these difficult cases of hip dysplasia.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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