The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 93, Issue Supplement 2

Scientific Articles | May 04, 2011

Computer-Assisted Correction of Cam-Type Femoroacetabular Impingement: A Sawbones Study

Sulaiman Almoussa, MD¹; Cefin Barton, MB BCh, MRCS(Ed), FRCS(Tr&Orth)¹; Andrew D. Speirs, MASc²; Wade Gofton, BScEd, MD¹; Paul E. Beaulé, MD, FRCSC¹

¹ Division of Orthopaedic Surgery, Ottawa Hospital, 501 Smyth Road, Ottawa, ON K1H 8L6, Canada. E-mail address for P.E. Beaulé: pbeaule@ottawahospital.on.ca
² Orthopaedic Biomechanics Lab, CHEO Research Institute I, Room 252, 401 Smyth Road, Ottawa, ON K1H 8L1, Canada

View Disclosures and Other Information

Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity.

Investigation performed at the Division of Orthopaedic Surgery, University of Ottawa, Ottawa, Ontario, Canada

J Bone Joint Surg Am, 2011 May 04;93(Supplement 2):70-75. doi: 10.2106/JBJS.J.01706

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Abstract

Background:

Assessing the adequacy of bone resection when correcting cam-type femoroacetabular impingement can be difficult when the surgeon is inexperienced or when less-invasive arthroscopic surgical techniques are used. The primary purpose of the present study was to compare, using a Sawbones model, the results of computer-assisted navigated osteochondroplasty of the femoral neck junction with correction with use of femoral head spherometer gauges. The second objective was to compare the results of computer-assisted osteochondroplasty performed by surgeons who had varied experience with the procedure.

Methods:

We calculated and compared the post-resection alpha angle in custom-molded Sawbones models with cam-type impingement following both surgical techniques, performed by three surgeons with varied experience with the procedure. The alpha angle was measured at two positions (the three o'clock and one-thirty positions of the femoral head-neck junction) before and after resection.

Results:

At the three o'clock position, there were no significant differences between the computer-navigation and spherometer groups (p = 0.83). There was undercorrection at the one-thirty position, with the median alpha angle being greater in the navigation group as compared with the spherometer group (71.0 compared with 58.6; p = 0.05). In the navigation group, there were no significant differences in the post-resection mean alpha angle among the three surgeons at either the one-thirty plane or the three o'clock plane.

Conclusions:

Navigation enabled the inexperienced surgeon to perform an equivalent amount of bone resection as the more experienced surgeons. However, all surgeons did not sufficiently resect the cam deformity as compared with the gold-standard open technique at the one-thirty position.

Clinical Relevance:

The limitations of computer-assisted surgery should be understood, and adequate training for surgical correction of cam-type femoroacetabular impingement remains essential.

Figures in this Article

Introduction

Introduction | Materials and Methods | Results | Discussion | References

Femoroacetabular impingement is secondary to premature contact between the proximal part of the femur and the acetabular rim, which causes damage to the labral-chondral junction and leads to hip pain¹. Ganz et al.² described two types of impingement: cam-type impingement, in which the femoral head is aspherical, and pincer-type impingement, which is secondary to either global (coxa profunda) or localized overcoverage (retroversion) of the acetabulum. Several clinical studies^3-7 have shown that surgical correction of these osseous abnormalities improves clinical function and relieves hip pain. The techniques for the surgical correction of both the cam and pincer types of femoroacetabular impingement have evolved rapidly over the last five years, with a greater emphasis being placed on less-invasive techniques such as hip arthroscopy⁸. This is especially true for the correction of cam deformities, in which the clinical results achieved with arthroscopic treatment^5,9,10 are comparable with the standard open-surgery technique involving the use of femoral spherometer gauges. Hip arthroscopy has the added advantage of less surgical morbidity and quicker patient recovery.

When correcting cam-type femoroacetabular impingement, the surgeon removes the protrusion at the femoral head-neck junction with use of a high-speed burr and/or osteotomes. This open resection is done with use of spherometer gauges to ensure the accuracy of the correction¹¹. However, the surgical dislocation technique has inherent risks related to surgical exposure, trochanteric nonunion, longer hospital stay, and the need for subsequent removal of implants^4,7. Although less-invasive techniques such as arthroscopy or a limited anterior approach can minimize the morbidity associated with the intervention, surgical-site visualization is more difficult, as is judging whether sufficient bone resection has been achieved¹². For the less-experienced surgeon, assessing the degree of the correction is more difficult and may lead to suboptimal results¹³. One potential intraoperative technique to minimize these problems is the use of computer-assisted surgery to assess the volume of bone resection needed for correction as well as the accuracy of the correction¹⁴.

The purpose of the present study was to compare the use of computer-assisted osteochondroplasty of the femoral head-neck junction with the use of an open technique involving spherometer gauges for the correction of a simulated cam impingement deformity in a Sawbones model. The secondary objective was to compare the result of computer-assisted osteochondroplasty performed by three surgeons who had varied experience with the procedure.

Materials and Methods

Introduction | Materials and Methods | Results | Discussion | References

A computer model of a medium Sawbones femur (Pacific Research Labs, Vashon, Washington) with a typical cam-type deformity in the anterosuperior region of the femoral head-neck junction was created. The model was used to custom-mold twelve fourth-generation medium Sawbones femora with the deformity; the deformity was based entirely within the cortical region of the Sawbones model (Fig. 1). A standard Sawbones model without the deformity was used as a normal reference for the registration step of the computer navigation system. The computer-assisted technique was applied with a mini anterior hip arthrotomy¹⁵ model because a model for hip arthroscopy with adjacent soft tissues was not feasible with use of Sawbones.

Fig. 1

Left: Photograph showing a normal Sawbones model (top) and custom-molded model with cam-type impingement (bottom). Right: Photograph showing the use of a standard spherometer gauge.

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Left: Photograph showing a normal Sawbones model (top) and custom-molded model with cam-type impingement (bottom). Right: Photograph showing the use of a standard spherometer gauge.

Sawbones Study Groups

The bone models were divided into four groups, with each group including three Sawbones models with the cam-type deformity. In Groups A, B, and C, the correction was performed with use of a computer-assisted technique through a mini-open anterior arthrotomy (Fig. 2). The procedures in each group were performed by surgeons with different levels of expertise; specifically, the procedures in Group A were performed by an experienced surgeon who specialized in the surgical correction of femoroacetabular impingement deformities, the procedures in Group B were performed by an experienced hip reconstruction surgeon who did not specialize in the treatment of young adults with hip disease, and the procedures in Group C were performed by a Fellow in adult reconstruction. The surgeon who performed the procedures in Group D was the same as the surgeon who procedures in Group A; however, in Group D, the correction was performed with use of the classic open technique with femoral head spherometer gauges (Fig. 1). In all cases, a high-speed burr was used to perform the bone resection.

Fig. 2

Photograph showing the simulated mini-open anterior approach.

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Photograph showing the simulated mini-open anterior approach.

Computer-Assisted Osteochondroplasty

A surgical navigation system with a femoroacetabular impingement module was used to guide resection of the deformity of the proximal part of each femur (BrainLAB AG, Feldkirchen, Germany). According to protocol, preoperative computed tomography (CT) scans were obtained for two Sawbones femoral models: one with cam deformity and the other with a standard Sawbones shape. The CT scan of the Sawbones model with the deformity was used for the registration step of the computer navigation. Each Sawbones model was inserted into a foam block with a simulated mini-open anterior approach and a lateral arthroscopic portal. A BrainLAB marker array was attached to the distal part of the femur. Computer registration for navigation was performed by capturing biplanar images of the proximal part of the femur with use of a fluoroscope (Siemens). An alpha angle of 45° was selected in the planning module as an indicator of adequate resection¹⁶. The navigation software highlighted in red the bone that was to be resected (Fig. 3). During the computer-assisted correction, the surgeon used a pointer with marker arrays to map the area of correction and to ensure that the red highlighted area, representing the bone deformity causing the cam impingement, was appropriately resected (Fig. 3).

Fig. 3

Computer-generated images of the axial and sagittal planes of the femoral head-neck junction. The navigation software highlighted in red the bone that was to be removed.

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Computer-generated images of the axial and sagittal planes of the femoral head-neck junction. The navigation software highlighted in red the bone that was to be removed.

Following osteochondroplasty, all femora underwent postoperative computed tomography scans. Preoperative, postoperative, and standard Sawbones CT scan data were automatically segmented (itksnap.org; version 1.8) to generate a three-dimensional surface model of each Sawbones. A sphere was fit to the joint surface of the femoral head using a least-squares fit (Gauss-Newton) with use of MATLAB (2007b; MathWorks, Natick, Massachusetts). The models were sliced in multiple planes in increments of 15°, rotated about the neck axis with use of Paraview software (Version 3.4; Kitware, Clifton Park, New York), to generate a profile of the intersection of the femoral surface with each plane (Fig. 4). The mean alpha angle values (and standard deviations) at both the one-thirty and three-o'clock planes of rotation¹⁷ were calculated and compared to identify differences between the different groups. To compare the results between the computer-assisted and open osteochondroplasty groups, the mean alpha angle values for Groups A and D (in which the procedures were performed by the same surgeon) at both the one-thirty and three-o'clock planes of rotation were compared.

Fig. 4

Left: The surface model of the proximal part of the femur was sliced with twelve planes, offset by 15° rotations about the neck axis. Plane orientations in the region of interest are shown. The blue and orange lines represent the coronal and axial oblique planes, respectively. Right: The alpha angle was measured in each plane with use of the neck axis as its first arm, with the second arm drawn from the best-fit circle anteriorly to the point where the head extended beyond the margin of the circle.

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Statistical Analysis

The accuracy of correction with use of navigation as compared with the open technique was assessed by comparing the post-resection alpha angles following the procedures that were performed by the same surgeon (i.e., Group A compared with Group D) with use of the Mann-Whitney U test. Differences in correction for Groups A, B, and C (that is, differences following procedures performed by different surgeons) were analyzed with use of the nonparametric Kruskal-Wallis test for independent samples. The corrections were assessed in the one-thirty and three-o'clock planes, and the level of significance was set at p < 0.05.

Results

Introduction | Materials and Methods | Results | Discussion | References

The median pre-correction alpha angles of the Sawbones femora with the cam deformity were 96° and 66° at the one-thirty and three-o'clock positions, respectively, compared with 62° and 38° for the normal standard Sawbones femora at the same positions. The post-resection alpha angle achieved with surgical navigation (Group A) was significantly higher than that achieved with open surgery and the use of spherometer gauges (Group D) at the one-thirty position (p = 0.05) but not at the three o'clock position (p = 0.83) (Fig. 5, Table I).

Fig. 5

Line graph showing the mean alpha angle measurements in the anterosuperior region for the three surgeons with navigation (A, B, C) and the standard open technique (D). The preoperative and normal femora are shown for reference. The one-thirty and three-o'clock planes used in the statistical analysis correspond to 45° and 90° orientation planes, respectively.

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TABLE I Alpha Angle Measurements in the One-Thirty and Three O'Clock Planes

	Alpha Angle Measurements (deg)
	One-Thirty Plane		Three O'Clock Plane
Group	Median	Range	Median	Range
Postop.
A	71.0	62.6 to 72.1	43.0	37.8 to 43.9
B	70.4	62.9 to 77.5	46.0	39.4 to 47.1
C	71.7	69.4 to 74.1	51.1	45.4 to 56.9
D	58.6	58.5 to 59.4	40.1	40.0 to 43.3
Preop.	95.7	—	65.5	—
Normal	62.1	—	38.0	—

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TABLE I Alpha Angle Measurements in the One-Thirty and Three O'Clock Planes

	Alpha Angle Measurements (deg)
	One-Thirty Plane		Three O'Clock Plane
Group	Median	Range	Median	Range
Postop.
A	71.0	62.6 to 72.1	43.0	37.8 to 43.9
B	70.4	62.9 to 77.5	46.0	39.4 to 47.1
C	71.7	69.4 to 74.1	51.1	45.4 to 56.9
D	58.6	58.5 to 59.4	40.1	40.0 to 43.3
Preop.	95.7	—	65.5	—
Normal	62.1	—	38.0	—

Computer-assisted osteochondroplasty showed similar post-resection alpha angles for all surgeons (Groups A, B, and C) in both the three o'clock and one-thirty planes (Fig. 5, Table I). No differences were found between surgeons in terms of post-surgical alpha angles at the one-thirty plane (p = 0.90) or the three o'clock plane (p = 0.21).

Discussion

Introduction | Materials and Methods | Results | Discussion | References

Open surgical dislocation of the hip has been a successful and reproducible technique for the treatment of cam-type femoroacetabular impingement^3,4,7. However, it is associated with some inherent morbidity, which can result in a lengthy recovery time, whereas less-invasive techniques are performed on outpatient basis, with comparable clinical results. However, it has been difficult to assess the adequacy of the resection of the cam deformity as undercorrection or overcorrection can compromise clinical results because of residual impingement¹³ and loss of the labral seal¹⁸, respectively. Some have suggested that the use of computer-assisted techniques¹⁴ could minimize the risks of surgical error as in other orthopaedic procedures¹⁹. The use of computer-assisted techniques could minimize the learning curve for the treatment of femoroacetabular impingement for the inexperienced surgeon. The present study showed that when using the surgical navigation software, all surgeons were able to accurately reduce the deformity through a mini-open, arthroscopic-assisted technique, suggesting a benefit of using computer navigation to permit the less-experienced surgeon to perform an equivalent amount of bone resection as the more experienced surgeons. However, the degree of correction achieved with use of the standard open technique was greater compared with that achieved with the less invasive, computer-assisted technique, with this being more evident at the one-thirty plane of rotation. Differing definitions of the hip center and spherical fit between the planning and analysis may have led to the differences in alpha angles. In addition, all surgeons resected less of the bump when compared with the "gold-standard" open technique at the one-thirty plane of rotation. This could have been due to a limitation of using a Sawbones model, which may not be an accurate morphologic representation of a human femur. However, in a recent publication defining the alpha angle in 200 asymptomatic volunteers, Hack et al.²⁰ found a 10° difference in average values when comparing the three o'clock and one-thirty positions, with values of 40.7° and 50.1°, respectively. Compared with the values for the unmodified Sawbones, the alpha angle was relatively close at the three o'clock position, with a value of 38°, whereas it was much larger at the one-thirty position, with a value of 62°. This may in part explain the relative undercorrection achieved at the one-thirty position, where the less-experienced surgeons may have been biased toward reproducing the "normal" Sawbones. Another, more likely, reason is the difficulty in properly visualizing the anterolateral femoral head-neck junction as well as the perception that this area is too lateral to be perceived as an area of impingement. Most likely, further development of femoroacetabular impingement computer-assisted software will require dynamic simulation of the impingement during motion in order to provide an overall better understanding of the pathological anatomy. Limitations in the accuracy of the correction could also be secondary to an imperfect registration step, indicating that the planning module requires a better confirmation process to assure the surgeon that the deformity is correctly localized.

The findings of the present study are consistent with the use of computer navigation in other surgical procedures; the use of navigation results in an immediate improvement in performance and accuracy and reduces outliers^19,21,22. While it appears that the continuous concurrent augmented feedback provided by this software improves surgical outcomes, its effect on learning has been questioned¹⁴ and remains unclear²³. For this reason, while computer navigation may improve the technical performance in osteochondroplasty, we believe that appropriate training in this procedure remains essential.

References

Introduction | Materials and Methods | Results | Discussion | References

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Ganz R; Parvizi J; Beck M; Leunig M; Nötzli H; Siebenrock KA. Femoroacetabular impingement: a cause for osteoarthritis of the hip. Clin Orthop Relat Res. 2003;417:112-20.[PubMed]

Beck M; Leunig M; Parvizi J; Boutier V; Wyss D; Ganz R. Anterior femoroacetabular impingement: part II. Midterm results of surgical treatment. Clin Orthop Relat Res. 2004;418:67-73.[CrossRef][PubMed]

Beaulé PE; Le Duff MJ; Zaragoza E. Quality of life following femoral head-neck osteochondroplasty for femoroacetabular impingement. J Bone Joint Surg Am. 2007;89:773-9.[CrossRef][PubMed]

Byrd JW; Jones KS. Arthroscopic femoroplasty in the management of cam-type femoroacetabular impingement. Clin Orthop Relat Res. 2009;467:739-46.[CrossRef][PubMed]

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Peters CL; Erickson JA. Treatment of femoro-acetabular impingement with surgical dislocation and débridement in young adults. J Bone Joint Surg Am. 2006;88:1735-41.[CrossRef][PubMed]

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Philippon MJ; Briggs KK; Yen YM; Kuppersmith DA. Outcomes following hip arthroscopy for femoroacetabular impingement with associated chondrolabral dysfunction: minimum two-year follow-up. J Bone Joint Surg Br. 2009;91:16-23.[CrossRef][PubMed]

Lavigne M; Parvizi J; Beck M; Siebenrock KA; Ganz R; Leunig M. Anterior femoroacetabular impingement: part I. Techniques of joint preserving surgery. Clin Orthop Relat Res. 2004;418:61-6.[CrossRef][PubMed]

Mardones R; Lara J; Donndorff A; Barnes S; Stuart MJ; Glick J; Trousdale R. Surgical correction of "cam-type" femoroacetabular impingement: a cadaveric comparison of open versus arthroscopic debridement. Arthroscopy. 2009;25:175-82.[CrossRef][PubMed]

May O; Matar WY; Beaulé PE. Treatment of failed arthroscopic acetabular labral debridement by femoral chondro-osteoplasty: a case series of five patients. J Bone Joint Surg Br. 2007;89:595-8.[CrossRef][PubMed]

Brunner A; Horisberger M; Herzog RF. Evaluation of a computed tomography-based navigation system prototype for hip arthroscopy in the treatment of femoroacetabular cam impingement. Arthroscopy. 2009;25:382-91.[CrossRef][PubMed]

Barton C; Banga K; Beaulé PE. Anterior Hueter approach in the treatment of femoro-acetabular impingement: rationale and technique. Orthop Clin North Am. 2009;40:389-95.[CrossRef][PubMed]

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Ganapathi M; Vendittoli PA; Lavigne M; Günther KP. Femoral component positioning in hip resurfacing with and without navigation. Clin Orthop Relat Res. 2009;467:1341-7.[CrossRef][PubMed]

Hack K; Di Primio G; Rakhra K; Beaulé PE. Prevalence of cam-type femoroacetabular impingement morphology in asymptomatic volunteers. J Bone Joint Surg Am. 2010;92:2436-44.[CrossRef][PubMed]

Cobb JP; Kannan V; Brust K; Thevendran G. Navigation reduces the learning curve in resurfacing total hip arthroplasty. Clin Orthop Relat Res. 2007;463:90-7.[PubMed]

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Topics

neck ; computers ; femur ; ostectomy ; femoral acetabular impingement ; osteochondroplasty

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Sulaiman Almoussa, Cefin Barton, Andrew D. Speirs, Wade Gofton, Paul E. Beaulé; Computer-Assisted Correction of Cam-Type Femoroacetabular ImpingementA Sawbones Study. The Journal of Bone & Joint Surgery. 2011 May;93(Supplement_2):70-75.

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