Purpose
To identify which hip pathomorphologies and motions are associated with a high fossa-foveolar mismatch (FFM) index.
Methods
Three-dimensional models of hips with femoroacetabular impingement syndrome or developmental dysplasia of the hip (DDH) and control hips were analyzed. Simulations of the physiological range of motion and impingement tests were performed using validated collision detection software. The FFM index—the proportion of the fovea tracking outside the acetabular fossa—was calculated for each motion.
Results
A total of 183 hips with femoroacetabular impingement syndrome and 22 control hips were included. DDH hips showed the highest FFM index (median 0.4), followed by hips with excessive femoral version (median 0.3). Controls had the lowest values (median 0.2). External rotation had the highest FFM in all groups. Motions such as flexion, extension, and abduction had the lowest FFM values.
Conclusions
DDH and excessive femoral version were linked to increased FFM, while hips from the control group presented the lowest mismatch. From all analyzed motions, the highest FFM was found in external rotation in all groups.
Level of Evidence
Level III, retrospective cohort study.
Lesions of the fossa-foveolar-ligamentous complex (LFFC) are remarkably common among young active patients undergoing hip joint–preserving surgery, as more than 9 of 10 patients are affected. , Increasing evidence suggests that lesions of the ligamentum teres (LT) in particular are not merely incidental findings but may be a clinically significant source of persistent intra-articular hip pain, contributing to mechanical symptoms such as instability, clicking, or locking. ,,, Research suggests that those lesions could be associated with adverse outcomes after hip arthroscopy. ,,, The underlying pathomechanisms have not been fully clarified. Klaue et al. initially suggested that LT degeneration could be due to a pathological positioning of the fovea capitis on the femoral head: the fossa-foveolar mismatch (FFM), defined by abnormal positioning of the fovea capitis outside the acetabular fossa during specific types of motions. This has been proposed as a possible mechanism for degenerative change around the LT, specifically including impingement of the LT between the lunate surface and the femoral head, as well as abnormal stress concentration at the cartilaginous edge of the acetabular fossa or fovea capitis. , The FFM index was introduced to quantify ligament-cartilage overlap. While it has been shown to be a reliable and reproducible measurement, little is known regarding its use to identify patient morphologies and specific motions at risk. The purpose of this study was to identify which hip pathomorphologies and motions are associated with a high fossa-foveolar mismatch index. We hypothesized that patients with version abnormalities and developmental dysplasia of the hip (DDH) would present higher FFM indices and that rotation motions would be associated with higher FFM indices.
Methods
The present 3-dimensional (3D) motion retrospective cohort study was approved by our institutional review board.
Patients
We assessed consecutive patients who had undergone joint-preserving surgery for femoroacetabular impingement syndrome (FAIS) or DDH at our home institution between November 2015 and May 2019. A total of 304 consecutive patients were evaluated for inclusion, and 183 hips were included in the final analysis ( Fig 1 ; Tables 1, 2 ). For the control group, we screened 205 patients who had undergone computed tomography (CT) angiography from June 2014 and December 2020. Twenty-four patients had previous surgery (osteosynthetic material or total hip arthroplasty), and 61 patients had an incomplete CT angiography that we could not use to generate a 3D model. Ninety-eight patients had femoral version pathology (<10 degrees or >25 degrees of femoral anteversion) or acetabular pathology (retroversion or lateral-center edge angle >33° or <22°) and were excluded. Therefore, 22 hips were included in the control group. Standardized preoperative anteroposterior pelvic radiographs were routinely performed in all patients. This allowed us to allocate hips to different study subgroups according to acetabular and femoral morphology using previously established reference values. ,
The Consolidated Standards of Reporting Trials flow diagram shows the inclusion and exclusion criteria for the study and control groups.
Table 1
Definition of the 6 Study Subgroups, Describing Distinct Acetabular and Femoral Pathomorphologies, and the Control Group According to Lerch et al
| Groups | Definition | Number of Hips | |
|---|---|---|---|
| Study subgroups | Dysplasia | LCEA <22° and/or anterior coverage <14% | 55 |
| Overcoverage | LCEA of 34°-39°, not all retroversion signs positive (posterior wall sign, crossover sign, ischial spine sign) | 34 | |
| Severe overcoverage | LCEA >39° and/or femoral head touching/crossing the ilioischial line and/or total femoral coverage >93% | 23 | |
| Retroversion | Crossover sign, ischial spine sign, and posterior wall sign positive, retroversion index >30% | 30 | |
| Deficient version | Femoral version angle <10° according to Murphy et al. | 28 | |
| Excessive version | Femoral version angle >25° according to Murphy et al. | 123 | |
| Cam-morphology | α angle >50° | 29 | |
| Control | Asymptomatic hips with CT scan for angiographic diagnostics and normal acetabular and femoral morphology: LCEA 23°-33°, femoral version angle 10°-25° according to Murphy et al. | 22 |
CY, computed tomography; LCE, lateral center-edge angle.
Table 2
Demographic and Radiologic Parameters of the Study Group (Consisting of 4 Acetabular and 3 Femoral Subgroups) and the Control Group (Consisting of 22 Asymptomatic Patients With a CT Scan for Angiography Diagnostics)
| Study Subgroups (n = 183) | Control Group (n = 22) | P Value | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Acetabular Morphology | Femoral Morphology | |||||||||
| Variables | Overall Study Group | Dysplasia (n = 55) | Overcoverage (n = 34) | Severe overcoverage (n = 23) | Retroversion (n = 30) | Cam-morphology (n = 29) | Deficient Femoral Version (n = 28) | Excessive Femoral Version (n = 123) | ||
| Demographics | ||||||||||
| Number of hips (patients) | 183 (155) | 55 (45) | 34 (33) | 23 (21) | 30 (30) | 29 (29) | 28 (24) | 123 (104) | 22 (22) | |
| Age at imaging, y |
28 ± 8
(15-54) |
30 ± 8
(18-50) |
26 ± 9
(16-54) |
29 ± 8
(18-50) |
25 ± 6
(16-36) |
28 ± 8 (18-50) |
28 ± 9
(15-54) |
27 ± 8
(16-50) |
55 ± 9
(37-66) |
<.001 |
| Sex (% men) | 38 (20) | 14 (26) | 9 (26) | 3 (13) | 9 (30) | 6 (21) | 11 (39) | 14 (11) | 16 (73) | <.001 |
| Side (% right) | 110 (59) | 36 (66) | 20 (59) | 11 (48) | 18 (60) | 23 (79) | 16 (57) | 75 (61) | 12 (55) | .699 |
| BMI |
24 ± 5
(17-39) |
25 ± 5
(18-39) |
25 ± 4
(19-36) |
25 ± 6
(17-34) |
24 ± 5
(17-34) |
24 ± 4 (19-33) |
27 ± 4
(20-36) |
24 ± 4
(17-39) |
27 ± 4
(19-33) |
.04 |
| Radiological | ||||||||||
| LCEA, ° |
28 ± 12
(–17 to 64) |
15 ± 6
(–17 to 22) |
36 ± 2
(34-39) |
47 ± 6
(40-61) |
31 ± 9
(9-51) |
28 ± 6 (10-38) |
33 ± 7
(19-55) |
27 ± 11
(17-61) |
33 ± 4
(25-39) |
<.001 |
| Extrusion index, % |
22 ± 11
(–6 to 67) |
34 ± 6
(22-67) |
15 ± 2
(10-18) |
6 ± 6
(–4 to 17) |
19 ± 8
(3-41) |
22 ± 6 (11-39) |
17 ± 6
(–4 to 29) |
23 ± 11
(–4 to 67) |
18 ± 4
(11-26) |
<.001 |
| Acetabular index, % |
5 ± 9
(–20 to 31) |
14 ± 6
(2-31) |
1 ± 5
(–12 to 11) |
-7 ± 5
(–14 to 5) |
2 ± 7
(–11 to 19) |
5 ± 8 (–19 to 20) |
4 ± 5
(–11 to 13) |
5 ± 10
(19-31) |
3 ± 5
(–6 to 9) |
<.001 |
| Crossover sign, % positive | 148 (79) | 38 (69) | 32 (94) | 19 (83) | 30 (100) | 21 (72) | 23 (82) | 97 (79) | 17 (77) | .04 |
| PW sign, % positive | 121 (65) | 45 (82) | 21 (62) | 10 (44) | 30 (100) | 22 (76) | 17 (61) | 75 (61) | 14 (64) | .001 |
| Ischial spine sign, % positive | 84 (45) | 21 (38) | 19 (56) | 12 (52) | 26 (87) | 15 (52) | 10 (37) | 50 (41) | 0 (0) | <.001 |
| Retroversion index, % |
15 ± 16
(0-77) |
10 ± 13
(0-54) |
23 ± 19
(0-77) |
21 ± 16
(0-53) |
42 ± 10
(31-77) |
17 ± 19 (0-49) |
12 ± 17
(0-77) |
15 ± 1
(0-57) |
18 ± 22
(0-70) |
<.001 |
| TAC, % |
77 ± 12
(32-100) |
64 ± 7
(32-76) |
84 ± 5
(74-93) |
94 ± 7
(77-100) |
78 ± 10
(58-100) |
77 ± 7 (65-93) |
82 ± 9
(67-100) |
76 ± 11
(32-100) |
83 ± 7
(62-94) |
<.001 |
| TPC, % |
44 ±
11 (10-83) |
37 ± 9
(16-55) |
46 ± 11
(10-66) |
54 ± 12
(35-77) |
36 ± 9
(16-61) |
43 ± 10 (21-61) |
48 ± 10
(29-74) |
44 ± 11
(10-77) |
50 ± 8
(32-63) |
<.001 |
| CCD, angle, ° |
137 ± 8
(117-161) |
138 ± 8
(126-157) |
140 ± 8
(129-161) |
134 ± 3
(128-139) |
136 ± 8
(120-158) |
135 ± 6 (126-158) |
134 ± 8
(117-146) |
138 ± 7
(121-161) |
134 ± 5
(124-140) |
.07 |
| α angle, ° |
53 ± 13
(30-120) |
54 ± 13
(34-120) |
50 ± 10
(36-75) |
44 ± 9
(31-73) |
52 ± 11
(30-79) |
62 ± 10 (52-100) |
54 ± 12
(31-75) |
53 ± 14
(30-120) |
.002 | |
| Femoral version, ° |
33 ± 18
(–11 to 72) |
36 ± 16
(–5 to 68) |
44 ± 9
(25-63) |
44 ± 7
(34-58) |
32 ± 18
(0-68) |
33 ± 15 (–4 to 57) |
1 ± 5
(–11 to 8) |
43 ± 9
(26-68) |
20 ± 5
(10-28) |
<.001 |
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