Knee Surg Sports Traumatol Arthrosc DOI 10.1007/s00167-015-3637-1
KNEE
The inferomedial patellar protuberance and medial patellar ossicle in patellar instability Simon T. Donell1 · Karen Shepherd1 · Kham Ali2 · Iain McNamara1
Received: 13 February 2015 / Accepted: 4 May 2015 © European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA) 2015
Abstract Purpose The purpose of the study was to define the frequency of an inferomedial patellar protuberance in patients presenting to a specialist Patella Clinic and to characterise the clinical and radiological features as well the association between the inferomedial patellar protuberance and the medial patellar ossicle. Methods A cohort of 163 patients (166 knees) was reviewed from a prospectively collected clinical database and radiological imaging. This included a record of patellar tracking. Results An inferomedial patellar protuberance was found in 62 (37 %) knees. A medial patellar ossicle was noted in 56 (34 %) knees. In all, an inferomedial patellar protuberance or medial patellar ossicle or both was found in 90 (54 %) knees. The association between inferomedial patellar protuberance and significant trochlear dysplasia was highly significant (p = 0.01), but not for the medial patellar ossicle (n.s.). The presence of an inferomedial patellar protuberance was significantly less likely in patients with hypermobility syndrome (p = 0.001); however, there was no significant association between hypermobility syndrome and medial patellar ossicle (n.s.), or the presence of either or both an inferomedial patellar protuberance and medial patellar ossicle (n.s.). All patients with a clunk at 20°–30° flexion had significant trochlear dysplasia and an inferomedial patellar protuberance.
* Simon T. Donell [email protected] 1
Department of Orthopaedics, Norfolk and Norwich University Hospital, Norwich NR14 8QD, UK
2
The George Washington University School of Medicine, Washington, DC, USA
Conclusion Radiological changes consistent with an inferomedial patellar protuberance were found in about one-third of patients presenting to a specialist Patella Clinic. Patellar maltracking and a clunk at 20°–30° flexion are associated with significant trochlear dysplasia plus an inferomedial patellar protuberance. If undertaking an operative correction, both deformities should be considered in order to avoid joint incongruity. Level of evidence III. Keywords Patella · Inferomedial protuberance · Medial patellar ossicle · Trochlear dysplasia · Patellar tracking · Classification
Introduction Patellofemoral dysplasia is well recognised as an important factor in patients presenting with patellar instability and maltracking. Recently, much has been discussed about the importance of trochlear dysplasia [1, 7], but little on any associated morphological abnormalities of the patella [5, 8]. In 2012, Vanhegan et al. [11] reported on a 16-yearold girl who presented with an inferomedial protuberance of the patellar causing “locking” of the knee. Anecdotally, this protuberance is relatively common in patients with trochlear dysplasia. In the Vanhegan et al. [11] case report, the images demonstrated trochlear dysplasia, although not noted by the authors, and there was no history reported of patellar dislocation. However, they did report that the patella moved laterally in the last 20° of extension, and was associated with a “clunk”. The locking was clearly a pseudo-locking. In 2012, Saragaglia et al. [9] reported on 26 cases of medial patellar dysplasia where they performed a medial
13
Knee Surg Sports Traumatol Arthrosc
facet patelloplasty. They described the radiological features solely from the skyline X-ray with a double outline on the medial side with a proximal medial facet and distal medial bulge. The bulge shows the patella incongruent with the trochlea. This lesion appears to be more severe than the one described by Vanhegan et al. [11]. However, Saraglia et al. [9] state in the text that the medial bulge is often distal. In over 20 years of seeing patients in a dedicated Patella Clinic and providing a supra-regional service for the management of complex patella problems, the experience of the senior author is that the inferomedial patellar protuberance (IPP) is relatively common in patients with trochlear dysplasia. The purpose of this study was to define the frequency of IPP in patients presenting to a specialist Patella Clinic and to characterise the clinical and radiological features and the association between the IPP and the medial patellar ossicle (MPO). The hypothesis was that an IPP is associated with significant trochlear dysplasia and the resultant incongruity may cause a clunk or pseudo-locking during the initial phase of knee flexion.
Materials and methods Fig. 1 Classification of patellar tracking
From January 2012 to July 2014, 173 patients with 176 affected knees presented to a dedicated Patella Clinic. Of these, nine patients were excluded because lack of suitable images on the Picture Archiving and Communication System (PACS) in five (foreign films not available in three, the patella was dislocated and not properly visualised in one, and one patient was pregnant), no skyline patella image in three, and nail-patella syndrome in one. The study population therefore consisted of 163 patients with data available on 166 knees. The data were collected using the Bluespier Data Management software (Bluespier Int, Droitwich, UK). Within this, a dedicated Patella Instability database has been created and includes records of the Beighton score [6], patellar apprehension, patellar tracking, range of movement, and mediolateral glide in extension [10]. Patellar apprehension was recorded with the knee resting in extension, the thumb applied to the medial border of the patella, and then pushed gently laterally. A positive result occurs if the quadriceps contracts; provocation of pain or discomfort without quadriceps contraction is not indicative of apprehension. The tracking of the patella was classified as shown in Fig. 1. This classification is based on clinical experience. A patella can track straight but be dislocatable in extension, especially in patients with joint laxity. For the study, the patient was defined as having a quadriceps lag if the active extension was less than the passive extension by 10°; the database records flexion angle is rounded to this figure.
13
The management program also keeps file attachments of the clinical notes, both outpatient and operative. Amongst the parameters noted were the patient’s age at operation, as well as the age at first-time patellar dislocation (FTPD), the presence of an inferomedial protuberance at operation, and the presence and site of any medial ossicle (MPO). Within the cohort, 34 deepening trochleoplasties were performed in 31 patients (25 females and six males) for recurrent patellar dislocation associated with significant trochlear dysplasia. These patients had intra-operative findings confirming the presence of an IPP and noting the site of an MPO. The radiological images were accessed through PACS (Synapse, Fujifilm UK Ltd, Bedford, UK). On the preoperative radiographs, the Dejour type [2] and boss height [3] were noted as well as the presence of an IPP. This was classified as Type 1 when the bony image shows a slight bony contour, but the operative findings found a significant cartilaginous component (Fig. 2), Type 2 when the bony contour was present and distinct, and Type 3 when the bony contour showed a posterior beak (Fig. 3). These were recorded for both the skyline and lateral views of the patella. An IPP radiologically was defined as the presence of Types 2 or 3 in either view, and the type chosen was the highest reported in either view. The presence and site of an MPO with respect to the medial border of the patella, and the Wiberg [13] type of the patella were also
Knee Surg Sports Traumatol Arthrosc Fig. 2 Lateral patellar X-ray and comparable intra-operative photograph showing a cartilaginous inferomedial patellar protuberance (Type 1)
Table 1 Presence of IPP and MPO by Wiberg type Wiberg type IPP Yes (%)a No MPO Yes (%)a No Either IPP/MPO/both Yes (%)a No
1
2
3
13 (25) 37
38 (42) 52
10 (40) 15
7 (14) 44
38 (42) 52
11 (44) 14
18 (35)
55 (61)
17 (68)
33
35
8
a
% of Wiberg type
Fig. 3 Classification of inferomedial patellar protuberance with illustrative lateral and tangential (skyline) views
noted. Significant trochlear dysplasia was defined as a boss height of >4 mm [4] in conjunction with a Type II or Type III trochlear dysplasia. The Bluespier Software Management system has National Research Ethical approval (London South-East ID no 11/LO/4107) for analysis for research purposes. Statistical analysis For comparisons between the radiological findings and trochlear dysplasia or Beighton score, the Chi-squared test was used. The Spearman’s rank correlation coefficient was applied to test associations between the IPP and patellar tracking. The level of significance was set at p
KNEE
The inferomedial patellar protuberance and medial patellar ossicle in patellar instability Simon T. Donell1 · Karen Shepherd1 · Kham Ali2 · Iain McNamara1
Received: 13 February 2015 / Accepted: 4 May 2015 © European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA) 2015
Abstract Purpose The purpose of the study was to define the frequency of an inferomedial patellar protuberance in patients presenting to a specialist Patella Clinic and to characterise the clinical and radiological features as well the association between the inferomedial patellar protuberance and the medial patellar ossicle. Methods A cohort of 163 patients (166 knees) was reviewed from a prospectively collected clinical database and radiological imaging. This included a record of patellar tracking. Results An inferomedial patellar protuberance was found in 62 (37 %) knees. A medial patellar ossicle was noted in 56 (34 %) knees. In all, an inferomedial patellar protuberance or medial patellar ossicle or both was found in 90 (54 %) knees. The association between inferomedial patellar protuberance and significant trochlear dysplasia was highly significant (p = 0.01), but not for the medial patellar ossicle (n.s.). The presence of an inferomedial patellar protuberance was significantly less likely in patients with hypermobility syndrome (p = 0.001); however, there was no significant association between hypermobility syndrome and medial patellar ossicle (n.s.), or the presence of either or both an inferomedial patellar protuberance and medial patellar ossicle (n.s.). All patients with a clunk at 20°–30° flexion had significant trochlear dysplasia and an inferomedial patellar protuberance.
* Simon T. Donell [email protected] 1
Department of Orthopaedics, Norfolk and Norwich University Hospital, Norwich NR14 8QD, UK
2
The George Washington University School of Medicine, Washington, DC, USA
Conclusion Radiological changes consistent with an inferomedial patellar protuberance were found in about one-third of patients presenting to a specialist Patella Clinic. Patellar maltracking and a clunk at 20°–30° flexion are associated with significant trochlear dysplasia plus an inferomedial patellar protuberance. If undertaking an operative correction, both deformities should be considered in order to avoid joint incongruity. Level of evidence III. Keywords Patella · Inferomedial protuberance · Medial patellar ossicle · Trochlear dysplasia · Patellar tracking · Classification
Introduction Patellofemoral dysplasia is well recognised as an important factor in patients presenting with patellar instability and maltracking. Recently, much has been discussed about the importance of trochlear dysplasia [1, 7], but little on any associated morphological abnormalities of the patella [5, 8]. In 2012, Vanhegan et al. [11] reported on a 16-yearold girl who presented with an inferomedial protuberance of the patellar causing “locking” of the knee. Anecdotally, this protuberance is relatively common in patients with trochlear dysplasia. In the Vanhegan et al. [11] case report, the images demonstrated trochlear dysplasia, although not noted by the authors, and there was no history reported of patellar dislocation. However, they did report that the patella moved laterally in the last 20° of extension, and was associated with a “clunk”. The locking was clearly a pseudo-locking. In 2012, Saragaglia et al. [9] reported on 26 cases of medial patellar dysplasia where they performed a medial
13
Knee Surg Sports Traumatol Arthrosc
facet patelloplasty. They described the radiological features solely from the skyline X-ray with a double outline on the medial side with a proximal medial facet and distal medial bulge. The bulge shows the patella incongruent with the trochlea. This lesion appears to be more severe than the one described by Vanhegan et al. [11]. However, Saraglia et al. [9] state in the text that the medial bulge is often distal. In over 20 years of seeing patients in a dedicated Patella Clinic and providing a supra-regional service for the management of complex patella problems, the experience of the senior author is that the inferomedial patellar protuberance (IPP) is relatively common in patients with trochlear dysplasia. The purpose of this study was to define the frequency of IPP in patients presenting to a specialist Patella Clinic and to characterise the clinical and radiological features and the association between the IPP and the medial patellar ossicle (MPO). The hypothesis was that an IPP is associated with significant trochlear dysplasia and the resultant incongruity may cause a clunk or pseudo-locking during the initial phase of knee flexion.
Materials and methods Fig. 1 Classification of patellar tracking
From January 2012 to July 2014, 173 patients with 176 affected knees presented to a dedicated Patella Clinic. Of these, nine patients were excluded because lack of suitable images on the Picture Archiving and Communication System (PACS) in five (foreign films not available in three, the patella was dislocated and not properly visualised in one, and one patient was pregnant), no skyline patella image in three, and nail-patella syndrome in one. The study population therefore consisted of 163 patients with data available on 166 knees. The data were collected using the Bluespier Data Management software (Bluespier Int, Droitwich, UK). Within this, a dedicated Patella Instability database has been created and includes records of the Beighton score [6], patellar apprehension, patellar tracking, range of movement, and mediolateral glide in extension [10]. Patellar apprehension was recorded with the knee resting in extension, the thumb applied to the medial border of the patella, and then pushed gently laterally. A positive result occurs if the quadriceps contracts; provocation of pain or discomfort without quadriceps contraction is not indicative of apprehension. The tracking of the patella was classified as shown in Fig. 1. This classification is based on clinical experience. A patella can track straight but be dislocatable in extension, especially in patients with joint laxity. For the study, the patient was defined as having a quadriceps lag if the active extension was less than the passive extension by 10°; the database records flexion angle is rounded to this figure.
13
The management program also keeps file attachments of the clinical notes, both outpatient and operative. Amongst the parameters noted were the patient’s age at operation, as well as the age at first-time patellar dislocation (FTPD), the presence of an inferomedial protuberance at operation, and the presence and site of any medial ossicle (MPO). Within the cohort, 34 deepening trochleoplasties were performed in 31 patients (25 females and six males) for recurrent patellar dislocation associated with significant trochlear dysplasia. These patients had intra-operative findings confirming the presence of an IPP and noting the site of an MPO. The radiological images were accessed through PACS (Synapse, Fujifilm UK Ltd, Bedford, UK). On the preoperative radiographs, the Dejour type [2] and boss height [3] were noted as well as the presence of an IPP. This was classified as Type 1 when the bony image shows a slight bony contour, but the operative findings found a significant cartilaginous component (Fig. 2), Type 2 when the bony contour was present and distinct, and Type 3 when the bony contour showed a posterior beak (Fig. 3). These were recorded for both the skyline and lateral views of the patella. An IPP radiologically was defined as the presence of Types 2 or 3 in either view, and the type chosen was the highest reported in either view. The presence and site of an MPO with respect to the medial border of the patella, and the Wiberg [13] type of the patella were also
Knee Surg Sports Traumatol Arthrosc Fig. 2 Lateral patellar X-ray and comparable intra-operative photograph showing a cartilaginous inferomedial patellar protuberance (Type 1)
Table 1 Presence of IPP and MPO by Wiberg type Wiberg type IPP Yes (%)a No MPO Yes (%)a No Either IPP/MPO/both Yes (%)a No
1
2
3
13 (25) 37
38 (42) 52
10 (40) 15
7 (14) 44
38 (42) 52
11 (44) 14
18 (35)
55 (61)
17 (68)
33
35
8
a
% of Wiberg type
Fig. 3 Classification of inferomedial patellar protuberance with illustrative lateral and tangential (skyline) views
noted. Significant trochlear dysplasia was defined as a boss height of >4 mm [4] in conjunction with a Type II or Type III trochlear dysplasia. The Bluespier Software Management system has National Research Ethical approval (London South-East ID no 11/LO/4107) for analysis for research purposes. Statistical analysis For comparisons between the radiological findings and trochlear dysplasia or Beighton score, the Chi-squared test was used. The Spearman’s rank correlation coefficient was applied to test associations between the IPP and patellar tracking. The level of significance was set at p
