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Fat pad entrapment at the hip: a new diagnosis.

Jayasekera N, Aprato A, Villar RN - PLoS ONE (2014)

Bottom Line: Both groups improved significantly after surgery at all time points.The fat pad found at the anterior head/neck junction of the hip joint can be a source of pain and we propose fat pad entrapment as a new, previously undescribed diagnosis.Level IV, case series.

View Article: PubMed Central - PubMed

Affiliation: Villar Bajwa Practice, Spire Cambridge Lea Hospital, Cambridge, United Kingdom.

ABSTRACT

Purpose: To establish if a positive impingement sign in femoroacetabular impingement (FAI) may result from entrapment of the fat pad located at the anterior head-neck junction of the upper femur. This fat pad is routinely removed before any cam lesion excision.

Methods: We report a prospective study of 142 consecutive hip arthroscopies for symptomatic FAI where the aim was to remove the arthroscopically identified area of impingement, not necessarily to create a spherical femoral head. Patients were divided into two groups. Group 1 (n = 92; 34 females, 58 males), where a cam-type bony FAI lesion was identified and excised in addition to the fat pad which overlay it, and Group 2 (n = 50; 29 females, 21 males) where the only identified point of impingement was a prominent fat pad. In this situation the fat pad was excised in isolation and the underlying bone preserved. Patients were assessed preoperatively, at six weeks, six months, one year and two years with a modified Harris hip score (mHHS).

Results: Both groups were comparable preoperatively for mean age, mean alpha angle and mean anterior offset ratio. Both groups improved significantly after surgery at all time points. However, Group 1 (fat pad and bone resection) demonstrated 16.0% improvement in mHHS by two years while for Group 2 (fat pad resection only) the improvement was 18.9% (p = 0.628).

Conclusions: The fat pad found at the anterior head/neck junction of the hip joint can be a source of pain and we propose fat pad entrapment as a new, previously undescribed diagnosis. Our findings also suggest that a large number of cam lesions are being excised unnecessarily and that further efforts should be made to understand the role of the fat pad as a source of groin discomfort.

Level of evidence: Level IV, case series.

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Related in: MedlinePlus

The labrum (white arrow) and prominent fat pad (black arrow) of a right hip.The anterolateral femoral head/neck junction as viewed from the peripheral compartment. Figure 2A. View of femoral head-neck junction and labrum. Figure 2B. Entrapment of the prominent fat pad with the hip in 90° flexion. Figure 2C. Excision of the fat pad almost complete and impingement between labrum and head-neck junction now relieved.
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pone-0083503-g002: The labrum (white arrow) and prominent fat pad (black arrow) of a right hip.The anterolateral femoral head/neck junction as viewed from the peripheral compartment. Figure 2A. View of femoral head-neck junction and labrum. Figure 2B. Entrapment of the prominent fat pad with the hip in 90° flexion. Figure 2C. Excision of the fat pad almost complete and impingement between labrum and head-neck junction now relieved.

Mentions: We investigated 142 consecutive patients who underwent arthroscopy of the hip for symptomatic FAI in the specialist practice of the senior author. All patients had a positive impingement test elicited by the senior author, and had failed to respond symptomatically to conservative treatment, which included activity modification, physiotherapy and treatment with nonsteroidal anti-inflammatory agents. A positive impingement test is defined as the finding of sharp pain in the ipsilateral groin on passive adduction and internal rotation of the hip held in at least 90° flexion [10]. All patients underwent standard anteroposterior (AP) pelvic and lateral hip radiographs and either MRI or MR arthrography within six months of their first outpatient visit. A cam-type impingement lesion was defined as abnormal asphericity or reduced offset of the anterolateral femoral head-neck junction, measured from the MRI scan using a digital goniometer and ruler before surgery to provide the alpha angle [15] and anterior offset ratio, [16], [17] respectively. Operations were performed under general anaesthetic in the lateral position with a specialist hip distractor (Lateral Hip Positioning System, Smith & Nephew Inc., Andover, Massachusetts, USA) [18]. Routine dynamic peroperative arthroscopic assessment was performed by repositioning the hip to 90 degrees of flexion. Impingement was deemed to be present if the labrum was seen to lift as the femoral head passed to and fro beneath it. By this means it was possible to identify arthroscopically the anatomical point at which impingement was occurring. On this basis, patients could be subdivided into two groups. Group 1, where a bony cam-type FAI lesion was seen to be the cause of impingement (Figures 1A and 1B), irrespective of whether or not a fat pad overlay it. For these patients, both the fat pad and the underlying bony lesion were excised with a combination of radiofrequency and a 5.5 mm high-speed spherical burr (Dyonics High Visibility Sheath Abrader Burr, Smith & Nephew Inc, Andover, Massachussets, USA). Group 2, however, comprised those patients where the only source of impingement was a prominent fat pad at the anterior femoral head/neck junction but where there was no evidence of a bony lesion impinging at all (Figures 2A, 2B and 2C). Even if a bony lesion was present, it could not be seen to form part of the impingement process during dynamic peroperative assessment under direct arthroscopic view. For these patients, only the fat pad was excised with a 90° radiofrequency tissue ablator (Dyonics RF-S Whirlwind, Smith & Nephew Inc, Andover, Massachussets, USA) but the underlying bone was preserved. For both groups, excision was considered complete when the femoral head/neck junction was seen to pass smoothly beneath the labrum on dynamic peroperative assessment without any points of impingement being seen. The aim of this procedure was to remove the area of impingement, not necessarily to create a spherical femoral head.


Fat pad entrapment at the hip: a new diagnosis.

Jayasekera N, Aprato A, Villar RN - PLoS ONE (2014)

The labrum (white arrow) and prominent fat pad (black arrow) of a right hip.The anterolateral femoral head/neck junction as viewed from the peripheral compartment. Figure 2A. View of femoral head-neck junction and labrum. Figure 2B. Entrapment of the prominent fat pad with the hip in 90° flexion. Figure 2C. Excision of the fat pad almost complete and impingement between labrum and head-neck junction now relieved.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3935831&req=5

pone-0083503-g002: The labrum (white arrow) and prominent fat pad (black arrow) of a right hip.The anterolateral femoral head/neck junction as viewed from the peripheral compartment. Figure 2A. View of femoral head-neck junction and labrum. Figure 2B. Entrapment of the prominent fat pad with the hip in 90° flexion. Figure 2C. Excision of the fat pad almost complete and impingement between labrum and head-neck junction now relieved.
Mentions: We investigated 142 consecutive patients who underwent arthroscopy of the hip for symptomatic FAI in the specialist practice of the senior author. All patients had a positive impingement test elicited by the senior author, and had failed to respond symptomatically to conservative treatment, which included activity modification, physiotherapy and treatment with nonsteroidal anti-inflammatory agents. A positive impingement test is defined as the finding of sharp pain in the ipsilateral groin on passive adduction and internal rotation of the hip held in at least 90° flexion [10]. All patients underwent standard anteroposterior (AP) pelvic and lateral hip radiographs and either MRI or MR arthrography within six months of their first outpatient visit. A cam-type impingement lesion was defined as abnormal asphericity or reduced offset of the anterolateral femoral head-neck junction, measured from the MRI scan using a digital goniometer and ruler before surgery to provide the alpha angle [15] and anterior offset ratio, [16], [17] respectively. Operations were performed under general anaesthetic in the lateral position with a specialist hip distractor (Lateral Hip Positioning System, Smith & Nephew Inc., Andover, Massachusetts, USA) [18]. Routine dynamic peroperative arthroscopic assessment was performed by repositioning the hip to 90 degrees of flexion. Impingement was deemed to be present if the labrum was seen to lift as the femoral head passed to and fro beneath it. By this means it was possible to identify arthroscopically the anatomical point at which impingement was occurring. On this basis, patients could be subdivided into two groups. Group 1, where a bony cam-type FAI lesion was seen to be the cause of impingement (Figures 1A and 1B), irrespective of whether or not a fat pad overlay it. For these patients, both the fat pad and the underlying bony lesion were excised with a combination of radiofrequency and a 5.5 mm high-speed spherical burr (Dyonics High Visibility Sheath Abrader Burr, Smith & Nephew Inc, Andover, Massachussets, USA). Group 2, however, comprised those patients where the only source of impingement was a prominent fat pad at the anterior femoral head/neck junction but where there was no evidence of a bony lesion impinging at all (Figures 2A, 2B and 2C). Even if a bony lesion was present, it could not be seen to form part of the impingement process during dynamic peroperative assessment under direct arthroscopic view. For these patients, only the fat pad was excised with a 90° radiofrequency tissue ablator (Dyonics RF-S Whirlwind, Smith & Nephew Inc, Andover, Massachussets, USA) but the underlying bone was preserved. For both groups, excision was considered complete when the femoral head/neck junction was seen to pass smoothly beneath the labrum on dynamic peroperative assessment without any points of impingement being seen. The aim of this procedure was to remove the area of impingement, not necessarily to create a spherical femoral head.

Bottom Line: Both groups improved significantly after surgery at all time points.The fat pad found at the anterior head/neck junction of the hip joint can be a source of pain and we propose fat pad entrapment as a new, previously undescribed diagnosis.Level IV, case series.

View Article: PubMed Central - PubMed

Affiliation: Villar Bajwa Practice, Spire Cambridge Lea Hospital, Cambridge, United Kingdom.

ABSTRACT

Purpose: To establish if a positive impingement sign in femoroacetabular impingement (FAI) may result from entrapment of the fat pad located at the anterior head-neck junction of the upper femur. This fat pad is routinely removed before any cam lesion excision.

Methods: We report a prospective study of 142 consecutive hip arthroscopies for symptomatic FAI where the aim was to remove the arthroscopically identified area of impingement, not necessarily to create a spherical femoral head. Patients were divided into two groups. Group 1 (n = 92; 34 females, 58 males), where a cam-type bony FAI lesion was identified and excised in addition to the fat pad which overlay it, and Group 2 (n = 50; 29 females, 21 males) where the only identified point of impingement was a prominent fat pad. In this situation the fat pad was excised in isolation and the underlying bone preserved. Patients were assessed preoperatively, at six weeks, six months, one year and two years with a modified Harris hip score (mHHS).

Results: Both groups were comparable preoperatively for mean age, mean alpha angle and mean anterior offset ratio. Both groups improved significantly after surgery at all time points. However, Group 1 (fat pad and bone resection) demonstrated 16.0% improvement in mHHS by two years while for Group 2 (fat pad resection only) the improvement was 18.9% (p = 0.628).

Conclusions: The fat pad found at the anterior head/neck junction of the hip joint can be a source of pain and we propose fat pad entrapment as a new, previously undescribed diagnosis. Our findings also suggest that a large number of cam lesions are being excised unnecessarily and that further efforts should be made to understand the role of the fat pad as a source of groin discomfort.

Level of evidence: Level IV, case series.

Show MeSH
Related in: MedlinePlus