Epidemiology of Patellofemoral joint pathologies, our experience at King Hussein Medical center

sitting ⁽²⁾. Although PFP is noticed in all age groups, it is noticed mainly in active aged less than 40 yrs patients ⁽³⁾.

 The causes of PFP have multiple factors. Increased patellofemoral joint exhaustion may be the cause of pain ⁽²⁾. Pathological configuration of the patellofemoral joint is incriminated in increased joint exhaustion. Different patellofemoral and bony configurations are correlated with PFP, such as increased quadriceps angle, increased sulcus angle, increased patellar tilt angle and increased lateral displacement ⁽²⁾.  Patellofemoral configuration characteristics are potentially changeable ⁽²⁾.

   Modifications in patellofemoral force induced by patellofemoral malconfiguration can be more than tissue force and lead to chondral insults and  patellofemoral osteoarthritis ( bone marrow insults, osteophytes, synovitis) ⁽²⁾. There were discrepancies in cartilage texture in females aged 18 - 45 yrs with PFP and patellar malconfiguration ⁽⁴⁾. T1 rho measurements were remarkably more in the lateral patellar facet in PFP with patellar tilt, having more proteoglycan loss ⁽⁴⁾. T1 rho measurements were almost equal to early OA ⁽⁴⁾. There is an association between trochlear bony configuration and patellofemoral OA ⁽²⁾. Patellofemoral malconfiguration is the cause of clinical features intensity in aged patients with knee OA ⁽⁵⁾. Patellofemoral malconfiguration can be associated with magnetic resonance imaging- textural characteristics of patellofemoral OA ( osteophytes and cartilage defects) in PFP.

    The goal of our investigation was to evaluate if patellofemoral joint  and bony configurations are correlated with cartilage, bone and soft tissue irregularities featured by MRI and with clinical patients features in PFP.

Methods

        This prospective investigation enrolled 105 patients with PFP, aged 18-55 yrs, of both genders (Table I) and who were assigned for MRI scan of the most painful knee, at King Hussein hospital, King Hussein medical center, Amman, JORDAN, during the period Jan 2018-Sep 2018 ,after obtaining approval from our local ethical and research board review committee of the Jordanian Royal medical services. Patients were grouped into two groups. Group I included (n= 50,47.6%)younger patients aged 18-26yrs and group II included (n=55,52.4%)older patients aged 46-55 yrs. Magnetic resonance imaging irregularities were recorded according to the Magnetic Resonance Imaging Osteoarthritis Knee Score. 

        Knee pain intensity was scored on a 10 verbal analog scale (usual pain included resting pain and worst pain included activity-induced pain) ⁽⁶⁾. Anterior Knee Pain Scale (AKPS; 0-10)⁽⁷⁾  showed lengthened sitting with knees flexed ⁽⁸⁾ . All patients were assigned for MRI scan of the most painful knee, positioned supine with the knee in 20° - 30° of flexion. All MRI scans were scored using the Magnetic Resonance Imaging Osteoarthritis Knee Score ⁽⁹⁾.  Scores of the most important elements included patellar cartilage irregularities, patellar osteophytes and Hoffa synovitis ⁽¹⁰⁾.

      Insall-Salvati ratio (is the ratio of patellar tendon length to oblique patellar length) ^(7,11-13);Trochlear angle is the angle between the posterior condylar line and a line along the most anterior margins of the medial and lateral trochlear facets; Patellar tilt angle is the angle between the posterior condylar line and the line via the maximal width of the patella; Lateral patellar tilt angle is the angle between the line parallel to the lateral patellar facet and the line connecting the most anterior points of the medial and lateral condyles and Sulcus angle is located between the condylar outsets. 

Statistics

   Pearson χ² and Student t tests were used to assess discrepancies between the groups. Associations between Magnetic Resonance Imaging Osteoarthritis Knee Score items and patellofemoral pain were assessed using regression analysis. Differences regarding age, gender and bilateral PFP were analyzed using linear regression, while ANOVA for period of PFP.P- values less than 0.05 were considered statistically significant.

Results

    The median age of group I patients was 21 yrs and of group II patients was 47 yrs, with preponderance of females (in group I: 27(54%)in group II:35(63.6%)) .Table I. Bilateral clinical knee picture was seen in 26(52%)of patients in group I and in 38(69.1%) of patients in group II. Sixteen patients (32%) and 4patients (7.3%) experienced a minimum clinical picture period of less than 6 months, in group I and II, respectively. Table I. Compared with the group II, group I showed remarkably younger PFP patients, less clinical picture period of less than 2 yrs and less bilateral features .Table I. Patients from  group II had less intense features on the verbal analog scale for pain and AKPS.

                Patellar cartilage irregularities were seen in 24 % and 10.9% of patients, with more irregularities in GI compared to GII. Table II. Patellar osteophytes were more commonly seen in GI (70%) in comparison to GII (58.2%). Hoffa synovitis was seen in 56%% and 63.6% of patients, in groups I and II, respectively. An increased IS ratio (patella alta) was correlated with patellar osteophytes and Hoffa synovitis. An increased patellar tilt angle (increased lateral tilt) was correlated with patellar cartilage irregularities and patellar osteophytes. Table III. There was a remarkable correlation between an increased sulcus angle (a shallower trochlea) and patellar osteophytes.

                 Sulcus angle was correlated with usual pain during running. Table IV. Aged patients were correlated with a smaller patellar tilt angle (P<0 .05) and smaller sulcus angle (P <0 .05). Females were correlated with larger patellar tilt angle (P <0 .05) and increased IS ratio (P< 0.05). Clinical features period more than 2 years was correlated with increased IS ratio (P<0.05), smaller sulcus angle (P<0.05) and smaller trochlear angle (P<0.05). Bilateral PFP was correlated with a larger patellar tilt angle (P<0.05), increased IS ratio (P< 0.05) and smaller trochlear angle (P< 0.05).

Table I. Patients characteristics.

 AKPS, Anterior Knee Pain Scale.

Table II.Anatomical configuration irregularities on MRI.

MOAKS, Magnetic Resonance Imaging Osteoarthritis Knee Score.

Table III. Correlation between configuration MRI irregularities and anatomical configuration recordings.

Table IV. Correlations between PFP pain and anatomical configurations.

Discussion

         There is a clear correlation between patellofemoral joint configuration and anatomical irregularities of the patellofemoral joint in patients with PFP. Increased IS ratio (patella alta), increased patellar tilt angle (increased lateral tilt) and increased sulcus angle ( a shallow trochlea) had increased signs of patellofemoral osteoarthritis on MRI, as patellar osteophytes and cartilage irregualarities. Age, gender, period of PFP and bilateral PFP were correlated with malconfiguration of the patellofemoral joint.

                     An increased IS ratio(patella alta) had the most correlation with configuration irregularities of the patellofemoral joint, as patellar osteophytes and Hoffa synovitis. IS ratio as a recording of configuration in aged patients is correlated with patellofemoral joint abnormality ⁽¹¹⁾. Abnormal lateral patellar is more common in patients with PFP with patella alta in comparison to patients having PFP with normal patellar height ⁽¹⁴⁾.An increased IS ratio was a risk factor for  patellofemoral cartilage distruction and bone marrow insults over 2.5 years ⁽⁵⁾. There is a positive correlation between an increased IS ratio and Hoffa synovitis . Fat pad is an active joint tissue which modulates inflammatory and destructive reactions in knee osteoarthritis ⁽⁵⁾. Markers of patellar instability were correlated with superolateral Hoffa fat pad edema in patients with knee pain ⁽¹⁴⁾. Abnormal configuration can lead to increased signal intensity of the fat pad, meaning fat pad edema and synovitis.

                    Increased lateral patellar location (tilt displacement) was correlated with increased configuration irregularities on MRI in the patellofemoral joint. Abnormal patellar configuration may decrease the contact area between the patella and trochlea, increasing patellofemoral joint stress in the lateral patellofemoral joint ⁽¹⁵⁾. Increased stress of the patellofemoral joint may decrease patellar cartilage thickness ⁽¹⁶⁾. Patellofemoral joint configuration can increase patellofemoral joint stress, as increased lateral patellar tilt angle was correlated with cartilage irregularities of the patella. In patellofemoral osteoarthritis patients, there were correlations between knee configuration and MRI findings of patellofemoral OA ⁽¹⁷⁾. Patellofemoral malconfiguration can cause increase patellofemoral joint stress, with structural configuration modifications in the joint (early OA signs). Patients with increased clinical features period and bilateral PFP had an increased IS ratio and increased sulcus angle in comparison to patients with reduced clinical features period and unilateral knee pain. There is subgroup of PFP patients liable to delayed patellofemoral osteoarthritis, because these configuration recordings are correlated with patellar osteophytes.

   PFP patients with patella alta or a shallow trochlea can develop more continuous clinical features ⁽¹⁸⁾.  Patella alta and lateral patellar tilt can benefit from nonoperative techniques ⁽¹⁹⁾.  Patients recruited in group I were younger with less clinical features period, but with worse pain in comparison to patients  in group II.There was strong correlations  between configuration recordings and shape irregularities ^(20,21).

In Conclusion

   For patients with PFP, some configuration recordings—as increased IS ratio (patella alta) and increased patellar tilt angle (increased lateral tilt) are correlated with patellar osteophytes, cartilage irregularities or Hoffa synovitis.

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