- Email: [email protected]
Therapeutic ablation of the infrapatellar fat pad under ultrasound guidance: a pilot study
Clinical Radiology (2007) 62, 1198e1201
Therapeutic ablation of the infrapatellar fat pad under ultrasound guidance: a pilot study C.V. House*, D.A. Connell Royal National Orthopaedic Hospital NHS Trust, Stanmore, Middlesex, UK Received 15 March 2007; received in revised form 28 June 2007; accepted 9 July 2007
AIM: To describe the technique of ablation of the infrapatellar fat pad using alcohol injection under ultrasound guidance and to assess the efficacy of the procedure in the relief of pain arising from fat pad impingement. MATERIAL AND METHODS: Consecutive patients with anterior knee pain and pathology in the infrapatellar fat pad, confirmed on magnetic resonance imaging (MRI), were enrolled in the study. A mixture of alcohol and local anaesthetic was injected under ultrasound guidance, with repeat injections at three-weekly intervals. Twelve patients (seven men, five women), mean age 30.8 years, underwent the procedure. Visual analogue scale pain scores were recorded before treatment and at the end of the treatment course. RESULTS: Before treatment, the mean (SD) pain score was 7.75 (1.14). Patients underwent a mean of four injections (range 2e6). After treatment, the mean pain score was 2.92 (2.61), representing a decrease of 62% (p < 0.001). Follow-up data were complete for all 12 patients. Other than short-lived pain at the time of injection, no serious side-effects were encountered. CONCLUSION: In patients with pain due to inflammation of the infrapatellar fat pad, ultrasound-guided alcohol ablation of the fat pad can provide effective symptom relief. The results of this pilot study indicate that a larger study is warranted to assess the long-term benefits of this well-tolerated procedure. ª 2007 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.
Introduction
Materials and methods
The syndrome of impingement of the infrapatellar fat pad was first described by Hoffa, in 1904.1 Magnetic resonance imaging (MRI) reliably demonstrates inflammation in the infrapatellar fat pad2,3 and enables exclusion of other significant pathology. Arthroscopic excision of the fat pad has been shown to alleviate symptoms and to improve function of the joint in patients with impingement.4 The aim of this pilot study was to examine the hypothesis that non-surgical ablation of the infrapatellar fat pad may similarly be beneficial.
Subjects and pain assessment
* Guarantor and correspondent: C.V. House, Department of Radiology, University College Hospital London NHS Trust, 235 Euston Road, London NW1 4BR, UK. Tel.: þ44 7710 352476; fax: þ44 20 7380 9068. E-mail address: [email protected] (C.V. House).
Twelve consecutive patients (seven men, five women) were enrolled in the study, for which research ethics committee approval was obtained. Informed consent was given. All patients had symptoms of anterior knee pain and a clinical diagnosis of fat pad impingement. Each underwent MRI of the knee, which confirmed the diagnosis by demonstrating focal abnormal high signal intensity on T2-weighted images of the infrapatellar fat pad (Fig. 1) and excluded any chondral, tendon, or bone injury. In three of the 12 patients, the signal abnormality was associated with a scar tract from previous arthroscopy. The mean age of the patients was 30.8 years (range 20e43 years) and the mean duration of symptoms was 20.8 months (range 6e48 months) before treatment. No patients were excluded from the study. Pain was assessed using the visual analogue scale (VAS), scoring pain from zero (no pain) to 10 (very
0009-9260/$ - see front matter ª 2007 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.crad.2007.07.005
Therapeutic ablation of the infrapatellar fat pad under ultrasound guidance
1199
ultrasound guidance, a 23-gauge needle was positioned in the infrapatellar fat pad via a percutaneous approach, targeting the site of signal abnormality on the MRI images (Fig. 2). The fat pad was infiltrated with 3 ml of a 1:10 solution of ethanol in bupivicaine (0.5%) and injections were repeated at 3-weekly intervals (the mean number of injections was four, range 2e6). The number of injections performed was based upon, and is comparable with, the number found to ablate neural tissue in the treatment of Morton’s neuroma.6,7
Statistical analysis Analysis of the change in VAS score between preand post-procedure, using the KolmogoroveSmirnov test, confirmed that there was no evidence of non-normality. The pre- and post-procedure VAS scores were compared using the paired sample
Figure 1 (a) Axial and (b) sagittal proton-density weighted, fat-saturated (PD-FS) MRI images demonstrating high signal intensity in the infrapatellar fat pad.
severe pain). The VAS as an instrument of measure presents a characteristic d in this case pain d as a continuum, rather than a series of discrete levels (e.g., mild, moderate, severe) and is of value in assessing the change of a subjective characteristic, such as pain, within individuals.5 Pain scores were recorded before treatment and at follow-up 6 weeks after completion of the treatment course, constituting the primary outcome measures in the study.
Ultrasound-guided injection Patients were positioned recumbent on the ultrasound couch. Under sterile conditions and using
Figure 2 (a) Longitudinal Doppler ultrasound image of the infrapatellar fat pad (arrowheads mark the anterior tibial plateau) demonstrates increased vascularity in the fat pad, corresponding to focal inflammation (arrow). (b) The needle tip is positioned in the infrapatellar fat under ultrasound guidance (arrows), targeting the area of abnormality detected on MRI.
1200
C.V. House, D.A. Connell
t-test. All statistical analysis was performed using SPSS for Windows, version 12.0 (Chicago, Illinois, USA) and p < 0.05 was considered statistically significant.
Results Follow-up and outcome Data were complete for each of the 12 patients enrolled in the study. The pre-treatment mean VAS pain score for the group of patients was 7.75 ( 1.14). At follow-up 6 weeks after completion of treatment, the mean pain score had fallen to 2.92 ( 2.61), a significant reduction of 62% (p < 0.001). Two patients experienced poor results, each with pain scores of 8 after ablation. It is noteworthy that both these patients had pain and MRI signal abnormality in the presence of arthroscopy scar tracts, though the numbers involved were too small to determine whether this was a significant observation. One patient was pain-free after ablation and a further three patients recorded VAS scores of 1 (Table 1). With the exception of shortlived, peri-procedural pain, no significant complications were encountered at the time of injection or during follow-up.
Discussion The infrapatellar fat pad (Hoffa’s fat pad) is a constant structure in the knee joint, consisting of a central body with medial and lateral extensions.8 Inferiorly, it is attached to the anterior horns of the medial and lateral menisci; its superior attachment is to the lower margin of the inferior pole of the patella. The fat pad is lined with synovium and has a rich neurovascular supply.
Table 1
The normal fat pad becomes flattened when the knee is extended. However, when hypertrophied after trauma, portions of the fat pad may impinge between the patellofemoral and femorotibial articular surfaces during extension.9 The cause of inflammation of the intrapatellar fat pad was not recorded in the present patient group, although others have found that either a single direct impact or twisting injury, or recurrent minor trauma may result in inflammation and impingement.3,4 Alternatively, impingement of the lateral infrapatellar fat pad may occur between the patellar tendon and lateral femoral condyle in the patellar tendonelateral femoral condyle syndrome, with resultant changes in the fat that are well identified using MRI.10 In three of the present patients, inflammation was related to an arthroscopic scar tract. It is postulated that in these patients, nerves lying in the infrapatellar fat becoming tethered by bands of scar tissue may also contribute to pain. MRI has high sensitivity for the detection of inflammation of the infrapatellar fat pad, and the location of signal abnormality on MRI was taken as the target for ablation.2 In the present study, ultrasound was used to guide injection and was not used as a diagnostic tool; however, during the course of the study sonographic abnormalities in the region of interest, including hypoechogenicity and neovascularity on colour Doppler, were noted (Fig. 2). Hoffa himself stressed the importance of conservative treatment before surgery was contemplated in cases of fat pad impingement. Conservative management, with a mean symptom duration of 21 months, had previously failed in the patients in the present study. The wide availability and high sensitivity of MRI, coupled with its ability to exclude other pathologies in the knee, makes a case for a re-assessment of traditional management of impingement. A search of the literature
Patient characteristics, pre- and post-treatment VAS pain scores
Age (years)/sex
Duration of symptoms (months)
Pathology
Pre-treatment VAS score
No. of injections
Post-treatment VAS score
43/F 29/M 20/M 23/F 34/M 35/F 29/M 32/M 28/F 36/M 38/M 23/F
24 48 6 24 14 24 18 20 26 14 8 24
Impingement Impingement Impingement Scar tract Impingement Impingement Scar tract Impingement Scar tract Impingement Impingement Impingement
8 9 7 8 6 7 7 8 10 7 7 9
3 6 2 3 4 5 4 4 5 4 5 3
2 1 0 8 2 2 1 3 8 1 3 4
Therapeutic ablation of the infrapatellar fat pad under ultrasound guidance
found no published data regarding the efficacy of conservative management of the condition. The success of surgical resection of the infrapatellar fat pad4 led to the hypothesis that non-surgical ablation of the fat pad might elicit a similar beneficial response. Several putative explanations exist to explain the efficacy of percutaneous ablation: sclerosis of the neovasculature in the fat pad may inhibit the inflammatory process; the direct neurotoxicity of the sclerosant may reduce pain; and ablation of the fat pad may reduce the volume of tissue and relieve impingement. The aim of this procedure was symptom control, not reversal of imaging abnormality, and follow-up imaging was not performed. It would seem likely that signal abnormality will persist and estimates of volume of the infrapatellar fat pad before and after treatment might present a further interesting line of research. The results of this pilot study, with a highly significant reduction in VAS pain scores after treatment, suggest that percutaneous, ultrasound-guided, targeted ablation of Hoffa’s fat pad does indeed relieve symptoms in patients with anterior knee pain due to inflammation of the fat pad. It is noted that two of the patients did not benefit from the procedure, but the reason for this is unclear. However, this rate of non-response mirrors exactly the post-surgical outcome reported in patients treated with arthroscopic resection4, in whom a subsequent diagnosis of a generalized inflammatory process, initially manifest as fat pad inflammation, was partially responsible for persistent symptoms after resection. In conclusion, impingement of the infrapatellar fat pad is a well-recognized cause of anterior knee
1201
pain. This pilot study suggests ablation of the fat pad using a series of alcohol injections is a procedure that is well-tolerated by the patient and which offers an efficacious, non-operative approach to treatment of impingement. Further studies, comparing fat pad ablation with surgical treatment, are warranted.
References 1. Hoffa A. Influence of adipose tissue with regard to the pathology of the knee joint. JAMA 1904;43:795e6. 2. Jacobson JA, Lenchik L, Ruhoy MK, et al. MR imaging of the infrapatellar fat pad of Hoffa. RadioGraphics 1997;17: 675e91. 3. Faletti C, de Stefano N, Giudice G, et al. Knee impingement syndromes. Eur J Radiol 1998;27(Suppl. 1):S60e9. 4. Ogilvie-Harris DJ, Giddens J. Hoffa’s disease: arthroscopic resection of the infrapatellar fat pad. Arthroscopy 1994; 10:184e7. 5. Wewers ME, Lowe NK. A critical review of visual analogue scales in the measurement of clinical phenomena. Res Nurs Health 1990;13:227e36. 6. Hughes RJ, Ali K, Jones H, et al. Treatment of Morton’s neuroma with alcohol injection under sonographic guidance: follow up of 101 cases. AJR Am J Roentgenol 2007;188: 1535e9. 7. Fanucci E, Masala S, Fabiano S, et al. Treatment of intermetatarsal Morton’s neuroma with alcohol injection under US guide: 10-month follow-up. Eur Radiol 2004; 14:514e8. 8. Gallagher J, Tierney P, Murray P, et al. The infrapatellar fat pad: anatomy and clinical correlations. Knee Surg Sports Traumatol Arthrosc 2005;13:268e72. 9. Magi M, Branca A, Bucca C, et al. Hoffa disease. Ital J Orthop Traumatol 1991;17:211e6. 10. Chung CB, Skaf A, Roger B, et al. Patellar tendon-lateral femoral condyle friction syndrome: MR imaging in 42 patients. Skeletal Radiol 2001;30:694e7.
Therapeutic ablation of the infrapatellar fat pad under ultrasound guidance: a pilot study C.V. House*, D.A. Connell Royal National Orthopaedic Hospital NHS Trust, Stanmore, Middlesex, UK Received 15 March 2007; received in revised form 28 June 2007; accepted 9 July 2007
AIM: To describe the technique of ablation of the infrapatellar fat pad using alcohol injection under ultrasound guidance and to assess the efficacy of the procedure in the relief of pain arising from fat pad impingement. MATERIAL AND METHODS: Consecutive patients with anterior knee pain and pathology in the infrapatellar fat pad, confirmed on magnetic resonance imaging (MRI), were enrolled in the study. A mixture of alcohol and local anaesthetic was injected under ultrasound guidance, with repeat injections at three-weekly intervals. Twelve patients (seven men, five women), mean age 30.8 years, underwent the procedure. Visual analogue scale pain scores were recorded before treatment and at the end of the treatment course. RESULTS: Before treatment, the mean (SD) pain score was 7.75 (1.14). Patients underwent a mean of four injections (range 2e6). After treatment, the mean pain score was 2.92 (2.61), representing a decrease of 62% (p < 0.001). Follow-up data were complete for all 12 patients. Other than short-lived pain at the time of injection, no serious side-effects were encountered. CONCLUSION: In patients with pain due to inflammation of the infrapatellar fat pad, ultrasound-guided alcohol ablation of the fat pad can provide effective symptom relief. The results of this pilot study indicate that a larger study is warranted to assess the long-term benefits of this well-tolerated procedure. ª 2007 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.
Introduction
Materials and methods
The syndrome of impingement of the infrapatellar fat pad was first described by Hoffa, in 1904.1 Magnetic resonance imaging (MRI) reliably demonstrates inflammation in the infrapatellar fat pad2,3 and enables exclusion of other significant pathology. Arthroscopic excision of the fat pad has been shown to alleviate symptoms and to improve function of the joint in patients with impingement.4 The aim of this pilot study was to examine the hypothesis that non-surgical ablation of the infrapatellar fat pad may similarly be beneficial.
Subjects and pain assessment
* Guarantor and correspondent: C.V. House, Department of Radiology, University College Hospital London NHS Trust, 235 Euston Road, London NW1 4BR, UK. Tel.: þ44 7710 352476; fax: þ44 20 7380 9068. E-mail address: [email protected] (C.V. House).
Twelve consecutive patients (seven men, five women) were enrolled in the study, for which research ethics committee approval was obtained. Informed consent was given. All patients had symptoms of anterior knee pain and a clinical diagnosis of fat pad impingement. Each underwent MRI of the knee, which confirmed the diagnosis by demonstrating focal abnormal high signal intensity on T2-weighted images of the infrapatellar fat pad (Fig. 1) and excluded any chondral, tendon, or bone injury. In three of the 12 patients, the signal abnormality was associated with a scar tract from previous arthroscopy. The mean age of the patients was 30.8 years (range 20e43 years) and the mean duration of symptoms was 20.8 months (range 6e48 months) before treatment. No patients were excluded from the study. Pain was assessed using the visual analogue scale (VAS), scoring pain from zero (no pain) to 10 (very
0009-9260/$ - see front matter ª 2007 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.crad.2007.07.005
Therapeutic ablation of the infrapatellar fat pad under ultrasound guidance
1199
ultrasound guidance, a 23-gauge needle was positioned in the infrapatellar fat pad via a percutaneous approach, targeting the site of signal abnormality on the MRI images (Fig. 2). The fat pad was infiltrated with 3 ml of a 1:10 solution of ethanol in bupivicaine (0.5%) and injections were repeated at 3-weekly intervals (the mean number of injections was four, range 2e6). The number of injections performed was based upon, and is comparable with, the number found to ablate neural tissue in the treatment of Morton’s neuroma.6,7
Statistical analysis Analysis of the change in VAS score between preand post-procedure, using the KolmogoroveSmirnov test, confirmed that there was no evidence of non-normality. The pre- and post-procedure VAS scores were compared using the paired sample
Figure 1 (a) Axial and (b) sagittal proton-density weighted, fat-saturated (PD-FS) MRI images demonstrating high signal intensity in the infrapatellar fat pad.
severe pain). The VAS as an instrument of measure presents a characteristic d in this case pain d as a continuum, rather than a series of discrete levels (e.g., mild, moderate, severe) and is of value in assessing the change of a subjective characteristic, such as pain, within individuals.5 Pain scores were recorded before treatment and at follow-up 6 weeks after completion of the treatment course, constituting the primary outcome measures in the study.
Ultrasound-guided injection Patients were positioned recumbent on the ultrasound couch. Under sterile conditions and using
Figure 2 (a) Longitudinal Doppler ultrasound image of the infrapatellar fat pad (arrowheads mark the anterior tibial plateau) demonstrates increased vascularity in the fat pad, corresponding to focal inflammation (arrow). (b) The needle tip is positioned in the infrapatellar fat under ultrasound guidance (arrows), targeting the area of abnormality detected on MRI.
1200
C.V. House, D.A. Connell
t-test. All statistical analysis was performed using SPSS for Windows, version 12.0 (Chicago, Illinois, USA) and p < 0.05 was considered statistically significant.
Results Follow-up and outcome Data were complete for each of the 12 patients enrolled in the study. The pre-treatment mean VAS pain score for the group of patients was 7.75 ( 1.14). At follow-up 6 weeks after completion of treatment, the mean pain score had fallen to 2.92 ( 2.61), a significant reduction of 62% (p < 0.001). Two patients experienced poor results, each with pain scores of 8 after ablation. It is noteworthy that both these patients had pain and MRI signal abnormality in the presence of arthroscopy scar tracts, though the numbers involved were too small to determine whether this was a significant observation. One patient was pain-free after ablation and a further three patients recorded VAS scores of 1 (Table 1). With the exception of shortlived, peri-procedural pain, no significant complications were encountered at the time of injection or during follow-up.
Discussion The infrapatellar fat pad (Hoffa’s fat pad) is a constant structure in the knee joint, consisting of a central body with medial and lateral extensions.8 Inferiorly, it is attached to the anterior horns of the medial and lateral menisci; its superior attachment is to the lower margin of the inferior pole of the patella. The fat pad is lined with synovium and has a rich neurovascular supply.
Table 1
The normal fat pad becomes flattened when the knee is extended. However, when hypertrophied after trauma, portions of the fat pad may impinge between the patellofemoral and femorotibial articular surfaces during extension.9 The cause of inflammation of the intrapatellar fat pad was not recorded in the present patient group, although others have found that either a single direct impact or twisting injury, or recurrent minor trauma may result in inflammation and impingement.3,4 Alternatively, impingement of the lateral infrapatellar fat pad may occur between the patellar tendon and lateral femoral condyle in the patellar tendonelateral femoral condyle syndrome, with resultant changes in the fat that are well identified using MRI.10 In three of the present patients, inflammation was related to an arthroscopic scar tract. It is postulated that in these patients, nerves lying in the infrapatellar fat becoming tethered by bands of scar tissue may also contribute to pain. MRI has high sensitivity for the detection of inflammation of the infrapatellar fat pad, and the location of signal abnormality on MRI was taken as the target for ablation.2 In the present study, ultrasound was used to guide injection and was not used as a diagnostic tool; however, during the course of the study sonographic abnormalities in the region of interest, including hypoechogenicity and neovascularity on colour Doppler, were noted (Fig. 2). Hoffa himself stressed the importance of conservative treatment before surgery was contemplated in cases of fat pad impingement. Conservative management, with a mean symptom duration of 21 months, had previously failed in the patients in the present study. The wide availability and high sensitivity of MRI, coupled with its ability to exclude other pathologies in the knee, makes a case for a re-assessment of traditional management of impingement. A search of the literature
Patient characteristics, pre- and post-treatment VAS pain scores
Age (years)/sex
Duration of symptoms (months)
Pathology
Pre-treatment VAS score
No. of injections
Post-treatment VAS score
43/F 29/M 20/M 23/F 34/M 35/F 29/M 32/M 28/F 36/M 38/M 23/F
24 48 6 24 14 24 18 20 26 14 8 24
Impingement Impingement Impingement Scar tract Impingement Impingement Scar tract Impingement Scar tract Impingement Impingement Impingement
8 9 7 8 6 7 7 8 10 7 7 9
3 6 2 3 4 5 4 4 5 4 5 3
2 1 0 8 2 2 1 3 8 1 3 4
Therapeutic ablation of the infrapatellar fat pad under ultrasound guidance
found no published data regarding the efficacy of conservative management of the condition. The success of surgical resection of the infrapatellar fat pad4 led to the hypothesis that non-surgical ablation of the fat pad might elicit a similar beneficial response. Several putative explanations exist to explain the efficacy of percutaneous ablation: sclerosis of the neovasculature in the fat pad may inhibit the inflammatory process; the direct neurotoxicity of the sclerosant may reduce pain; and ablation of the fat pad may reduce the volume of tissue and relieve impingement. The aim of this procedure was symptom control, not reversal of imaging abnormality, and follow-up imaging was not performed. It would seem likely that signal abnormality will persist and estimates of volume of the infrapatellar fat pad before and after treatment might present a further interesting line of research. The results of this pilot study, with a highly significant reduction in VAS pain scores after treatment, suggest that percutaneous, ultrasound-guided, targeted ablation of Hoffa’s fat pad does indeed relieve symptoms in patients with anterior knee pain due to inflammation of the fat pad. It is noted that two of the patients did not benefit from the procedure, but the reason for this is unclear. However, this rate of non-response mirrors exactly the post-surgical outcome reported in patients treated with arthroscopic resection4, in whom a subsequent diagnosis of a generalized inflammatory process, initially manifest as fat pad inflammation, was partially responsible for persistent symptoms after resection. In conclusion, impingement of the infrapatellar fat pad is a well-recognized cause of anterior knee
1201
pain. This pilot study suggests ablation of the fat pad using a series of alcohol injections is a procedure that is well-tolerated by the patient and which offers an efficacious, non-operative approach to treatment of impingement. Further studies, comparing fat pad ablation with surgical treatment, are warranted.
References 1. Hoffa A. Influence of adipose tissue with regard to the pathology of the knee joint. JAMA 1904;43:795e6. 2. Jacobson JA, Lenchik L, Ruhoy MK, et al. MR imaging of the infrapatellar fat pad of Hoffa. RadioGraphics 1997;17: 675e91. 3. Faletti C, de Stefano N, Giudice G, et al. Knee impingement syndromes. Eur J Radiol 1998;27(Suppl. 1):S60e9. 4. Ogilvie-Harris DJ, Giddens J. Hoffa’s disease: arthroscopic resection of the infrapatellar fat pad. Arthroscopy 1994; 10:184e7. 5. Wewers ME, Lowe NK. A critical review of visual analogue scales in the measurement of clinical phenomena. Res Nurs Health 1990;13:227e36. 6. Hughes RJ, Ali K, Jones H, et al. Treatment of Morton’s neuroma with alcohol injection under sonographic guidance: follow up of 101 cases. AJR Am J Roentgenol 2007;188: 1535e9. 7. Fanucci E, Masala S, Fabiano S, et al. Treatment of intermetatarsal Morton’s neuroma with alcohol injection under US guide: 10-month follow-up. Eur Radiol 2004; 14:514e8. 8. Gallagher J, Tierney P, Murray P, et al. The infrapatellar fat pad: anatomy and clinical correlations. Knee Surg Sports Traumatol Arthrosc 2005;13:268e72. 9. Magi M, Branca A, Bucca C, et al. Hoffa disease. Ital J Orthop Traumatol 1991;17:211e6. 10. Chung CB, Skaf A, Roger B, et al. Patellar tendon-lateral femoral condyle friction syndrome: MR imaging in 42 patients. Skeletal Radiol 2001;30:694e7.