Comparison of patellofemoral outcomes after TKA using two prostheses with different patellofemoral design features

Purpose

The purpose of the present study was to compare the clinical and radiographic results after TKA using two prostheses with different sagittal patellofemoral design features, including outcomes related to compatibility of the patellofemoral joint.

Methods

The clinical and radiographic results of 81 patients (100 knees) who underwent TKA using the specific prosthesis (group A) were compared with those in a control group who underwent TKA using the other prosthesis (group B). The presence of anterior knee joint pain, patellar crepitation, and patellar clunk syndrome was also checked.

Results

The function score and maximum flexion angle at the last follow-up were slightly better in group A than those in group B (92.0 ± 2.3 vs. 90.6 ± 4.2) (133.6° ± 8.4° vs. 129.6° ± 11.4°). Anterior knee pain was observed in 6 knees and patellar crepitation in four knees in group A. In group B, these symptoms were observed in 22 knees and 18 knees, respectively. There was no patellar clunk syndrome in either group. The alignment was corrected with satisfactory positioning of components. The patellar height remained unchanged after TKA in the two groups. The differences between preoperative and postoperative patellar tilt angle and patellar translation were small.

Conclusion

When comparing the clinical and radiographic results after TKA using two prostheses with different sagittal patellofemoral design features, TKA using the specific prosthesis provided satisfactory results with less clinical symptoms related to the patellofemoral kinematics with TKA using the other prosthesis.

Level of evidence

III.

     

Allowing one quadrant of patellar lateral translation during medial patellofemoral ligament reconstruction successfully limits maltracking without overconstraining the patella

Purpose

Graft tensioning during medial patellofemoral ligament (MPFL) reconstruction typically allows for lateral patellar translation within the trochlear groove. Computational simulation was performed to relate the allowed patellar translation to patellofemoral kinematics and contact pressures.

Methods

Multibody dynamic simulation models were developed to represent nine knees with patellar instability. Dual limb squatting was simulated representing the pre-operative condition and simulated MPFL reconstruction. The graft was tensioned to allow 10, 5, and 0 mm of patellar lateral translation at 30° of knee flexion. The patellofemoral contact pressure distribution was quantified using discrete element analysis.

Results

For the 5 and 10 mm conditions, patellar lateral shift decreased significantly at 0° and 20°. The 0 mm condition significantly decreased lateral shift for nearly all flexion angles. All graft conditions significantly decreased lateral tilt at 0°, with additional significant decreases for the 5 and 0 mm conditions. The 0 mm condition significantly increased the maximum medial pressure at multiple flexion angles, increasing by 57% at 30°, but did not alter the maximum lateral pressure.

Conclusions

Allowing 5 to 10 mm of patellar lateral translation limits lateral maltracking, thereby decreasing the risk of post-operative recurrent instability. Allowing no patellar translation during graft tensioning reduces maltracking further, but can overconstrain the patella, increasing the pressure applied to medial patellar cartilage already fibrillated or eroded from an instability episode.

     

Comparative analysis of medial patellofemoral ligament length change pattern in patients with patellar dislocation using open-MRI

Purpose

Medial patellofemoral ligament (MPFL) reconstruction has become a common form of treatment for recurrent patellar dislocation. This study was performed using open-MRI to compare the length change pattern of MPFL in patients with a history of patellar dislocation to that in healthy subjects.

Methods

The subjects comprised 10 knees of 8 males and 13 knees of 12 females with a history of one or more patellar dislocations. The length of the MPFL was measured using open-MRI in both the leg-extended position and knee-flexed positions to analyse the length change pattern.

Results

The average MPFL lengths were 58.6 ± 6.5 mm and 52.0 ± 4.6 mm for males and females in the extended knee position, respectively. The length change pattern of the MPFL showed slight variation up to a flexion angle of 30° and a clear decrease above 30°. This pattern differed from that of normal MPFL. In terms of morphology, the fibre bundle of the damaged MPFL followed a convex course towards the side of the patellofemoral joint surface at a knee flexion angle of 60°, whereas that of the normal MPFL followed a straight course.

Conclusion

The in vivo damaged MPFL length change pattern was specific and differed distinctly from that of normal MPFL. The results of the present study suggested that MPFL fibres with a history of patellar dislocation lack sufficient tension at knee flexion angles of 0°–60°. However, further studies are needed to obtain a better understanding of cases with a patellar dislocation or postsurgical cases of MPFL reconstruction.

Level of evidence

III.

     

The horizontal Y-shaped graft with respective graft tension angles in anatomical two-bundle medial patellofemoral ligament reconstruction

Purpose

Various techniques for medial patellofemoral ligament (MPFL) reconstruction have been described with two bundles of graft tensioned simultaneously. The present study was to introduce an anatomical reconstruction procedure using a horizontal Y-shaped graft with respective graft tension angles and report the preliminary results.

Methods

A surgical technique for MPFL reconstruction using a horizontal Y-shaped semitendinosus tendon autograft with two bundles tensioned at 0° and 30° of knee flexion was described in detail. The patellar stability was evaluated with the apprehension test and an axial computed tomography (CT) scan at 30° of knee flexion. The knee function was evaluated using the Lysholm and Kujala scores.

Results

No recurrent dislocation or subluxation was reported for 45 patients at a mean of 33.7-month follow-up. On CT images, congruence angle, patellar tilt angle, lateral patellar angle and lateral displacement were restored to the normal range. At the last follow-up, the mean Lysholm score improved from 51.8 ± 6.2 to 91.7 ± 4.1 and mean Kujala score was from 53.4 ± 5.3 to 90.9 ± 6.6 (P < 0.01).

Conclusions

The present anatomical MPFL reconstruction technique with a horizontal Y-shaped two-bundle graft tensioned at respective knee flexion angles could not only recreate the fan-shape of MPFL but also mimic the function bundles of native ligament. Clinical follow-up confirms the good restoration of the patellar stability and significant improvement of knee function without special complications.

Level of evidence

Therapeutic, Level IV.

     

Patellar tracking should be taken into account when measuring radiographic parameters for recurrent patellar instability

Purpose

To date, many radiographic parameters on patellar instability have their measurements taken statically, and have not been studied in various degrees of flexion according to the patellar tracking. There are also limited data regarding the use of these parameters in predicting recurrent patellar dislocation. The current study aims to review the radiographic parameters of the patellofemoral joint in different degrees of knee flexion and to correlate them with the presence of recurrent instability.

Methods

A 10-year retrospective study was conducted on all patients who had computed tomography patellar-tracking scan done for patellar instability when aged 18 years or younger. The computed tomography patellar-tracking scans were performed with the knee in extension, 10° flexion, and 20° flexion. The axial radiographic parameters were evaluated at the patellar equator, roman arch, and distal patellar pole. Sagittal and coronal parameters were noted. Radiographic parameters were then correlated with recurrent patellar instability.

Results

The femoral sulcus angle and trochlear groove depth at the distal patellar pole in 10° knee flexion (p value 0.04 and 0.03, respectively) and patellar equator in 20° knee flexion (p value 0.02 and 0.03, respectively) had the most significant clinical correlations with recurrent instability on multivariate analysis. Other radiographic parameters found to have significant clinical correlation on univariate analysis include the patellar tilt angle, congruence angle, femoral sulcus angle, trochlear groove depth, and Wiberg’s classification.

Conclusions

As per the knee dynamics, axial radiographic parameters had the most significant correlation with recurrent patellar instability when measured at the distal patellar pole in 10° knee flexion and at the patellar equator in 20° knee flexion. Future axial radiographic evaluation of patellofemoral instability should then be performed at these degrees of knee flexion and axial cuts. Trochlear dysplasia, as measured by the femoral sulcus angle and trochlear groove depth, was the most significant predictor of recurrent patellar instability in the skeletally immature. Wiberg’s classification was also a novel factor found to have clinical correlation with patellofemoral instability.

Level of evidence

III.

     

Sagittal plane tilting deformity of the patellofemoral joint: a new concept in patients with chondromalacia patella

Purpose

The aims of this study were to evaluate sagittal plane alignment in patients with chondromalacia patella via magnetic resonance imaging (MRI), analyse the relationships between the location of the patellar cartilaginous lesions and sagittal alignment and finally investigate the relationships between the sagittal plane malalignment and patellofemoral loadings using by finite element analysis.

Methods

Fifty-one patients who were diagnosed with isolated modified Outerbridge grade 3–4 patellar chondromalacia based on MRI evaluation and 51 control subjects were evaluated. Chondromalacia patella patients were divided into three subgroups according to the chondral lesion location as superior, middle and inferior. The patella–patellar tendon angle (P–PT) was used for evaluation of sagittal alignment of patellofemoral joint. Each subgroup was compared with control group by using P–PT angle. To investigate the biomechanical effects of sagittal plane malpositioning on patellofemoral joint, bone models were created at 30°, 60° and 90° knee flexion by using mean P–PT angles, which obtained from patients with chondromalacia patellae and control subjects. The total loading and contact area values of the patellofemoral joints were investigated by finite element analysis.

Results

The mean age of all participants was 52.9 ± 8.2 years. The mean P–PT angle was significantly lower in chondromalacia group (142.1° ± 3.6°) compared to control group (144.5° ± 5.3°) (p = 0.008). Chondral lesions were located in superior, middle and inferior zones in 16, 20 and 15 patients, respectively. The mean P–PT angles in patients with superior (141.8 ± 2.7) and inferior subgroups (139.2 ± 2.3) were significantly lower than the values in the control group (p < 0.05). The contact area values were detected higher in models with chondromalacia than in the control models at the same flexion degrees. There were increased loadings at 30° and 90° flexions in the sagittal patellar tilt models.

Conclusion

This study revealed that sagittal plain malpositioning of the patellofemoral joint might be related to chondromalacia, especially in the presence of lesions in the upper and lower part of the patella. This condition leads to supraphysiological loadings on the patellofemoral joint. Sagittal patellar tilt should be considered in the evaluation and management of patellar cartilage defects. Taking sagittal plane malalignment into consideration in patellofemoral joint evaluation will enable us to design new physical and surgical modalities.

Level of evidence

IV.

     

Patellofemoral arthrodesis as pain relief in extreme patella alta

Purpose

There is no golden standard management for neglected, chronic patellar tendon rupture as they are fairly rare. Nevertheless, accompanying pain can be highly debilitating. By presenting a case of patellar tendon repair, the exceptional results of a patellofemoral arthrodesis are described.

Methods

A patient presented herself with a sustained patellar tendon rupture which was neglected for several years, causing a complete extensor mechanism dysfunction. Her most debilitating complaint was pain. As ligament reconstruction in this case was not possible, patellofemoral arthrodesis was aimed for. The pain resulting from micromotions was subsided by implementing a unique technique using a lock-key principle to obtain a patellofemoral arthrodesis.

Results

The procedure proceeded without complications. The patient followed a regular post-operative plan and is now successful in maximum weight bearing her knee without pain.

Conclusions

A patellofemoral arthrodesis can be regarded safe and also very effective in the relief of pain in extreme patella alta.

Level of evidence

Therapeutic studies, Level IV.

     

The anatomy and isometry of a quasi-anatomical reconstruction of the medial patellofemoral ligament

Purpose

To describe the anatomy of the medial patellofemoral ligament (MPFL) and its relationship to the Adductor Magnus (AM) tendon as well as the behaviour exhibited in length changes during knee flexion.

Methods

Ten cadaveric knees were dissected. The length from the superior and inferior patellar origin of the MPFL to its femoral insertion was measured at different degrees of knee flexion (0°, 30°, 60°, 90° and 120°). The same measures were made from both patellar origins of the MPFL up to the femoral insertion of the AM. The distance between the insertion of the AM and the Hunter canal was also measured.

Results

In general, isometry up to 90° was seen in all measures of the MPFL and those of the AM. The most isometric behaviour was seen in 2 measures: the length of the AM femoral insertion up to the inferior origin of the MPFL on the patella and the length of the femoral insertion of the MPFL up to the inferior origin of the MPFL on the patella. Similar behaviour was seen regardless of the anatomical or quasi-anatomical femoral point of attachment (n.s.). The distance from the AM tendon to the Hunter canal had a mean value of 78.6 mm (SD 9.4 mm).

Conclusion

The behaviour exhibited during the changes in the length of the anatomical femoral footprint of the MPFL and the AM is similar. Neurovascular structures were not seen at risk. This is relevant in the daily clinical practice since the AM tendon might be a suitable point of insertion for MPFL reconstruction.

     

Impact of the patella height on the strain pattern of the medial patellofemoral ligament after reconstruction: a computer model-based study

Purpose

Medial patellofemoral ligament (MPFL) reconstruction is a key procedure for treating patellofemoral instability. However, controversy exists regarding the correct graft placement in different patellar heights. Therefore, our study aimed to investigate the influence of patellar height on MPFL insertion points.

Methods

Strain patterns of the reconstructed MPFL were calculated using a dynamic musculoskeletal multibody simulation. Numerous patellar (proximal, central, distal) and femoral attachment sites (around the radiological point according to Schöttle) were analysed in the presence of different patella heights [Insall–Salvati (IS) indices 0.74, 1.0, 1.5] during dynamic knee flexion from 0° to 120°.

Results

The reconstructed MPFL showed an almost isometric behaviour at the anatomic insertion (IS 1.0). Slight variation (<5 mm) around the ideal femoral insertion point resulted in only small changes in MPFL tension. However, a displacement of 10 mm led to a significant increase in MPFL tension, especially in the more anteriorly/proximally located femoral attachment points. Depending on the patella height, there exists an area of absolute isometry of the MPFL (length change <3 %) on the femoral condyle, which did not necessarily coincide exactly with the radiological point, but was located within a radius of 5 mm around it.

Conclusions

When reconstructed in the radiological femoral insertion point, MPFL strain patterns were only slightly affected by different patella heights (IS 0.74–1.5) suggesting that MPFL reconstruction could be safely performed using the radiological insertion. However, in case of a patella alta (IS 1.5), a slightly more proximal femoral insertion is beneficial for the biomechanical behaviour of the reconstructed MPFL.

     

Femoral insertion site of the graft used to replace the medial patellofemoral ligament influences the ligament dynamic changes during knee flexion and the clinical outcome

Purpose

This study’s purpose was to investigate how an ideal anatomic femoral attachment affects the dynamic length change pattern of a virtual medial patellofemoral ligament (MPFL) from an extended to a highly flexed knee position; to determine the relative length and length change pattern of a surgically reconstructed MPFL; and to correlate femoral attachment positioning, length change pattern, and relative graft length with the clinical outcome.

Methods

Twenty-four knees with isolated nonanatomic MPFL reconstruction were analysed by three-dimensional computed tomography at 0°, 30°, 60°, 90°, and 120° of knee flexion. The lengths of the MPFL graft and a virtual anatomic MPFL were measured. The pattern of length change was considered isometric if the length distance changed <5 mm through the entire dynamic range of motion.

Results

Knee flexion significantly affected the path lengths between the femoral and patellar attachments. The length of the anatomic virtual MPFL decreased significantly from 60° to 120°. Its maximal length was 56.4 ± 6.8 mm at 30°. It was isometric between 0° and 60°. The length of the nonanatomic MPFL with a satisfactory clinical result decreased during flexion from 0° to 120°. Its maximal length was 51.6 ± 4.6 mm at 0° of knee flexion. The lengths measured at 0° and 30° were isometric and statistically greater than the lengths measured at higher flexion degrees. The failed nonanatomic MPFL reconstructions were isometric throughout the dynamic range, being significantly shorter (27.1 ± 13.3 %) than anatomic ligaments.

Conclusion

The femoral attachment point significantly influences the relative length and the dynamic length change of the grafts during knee flexion–extension and graft isometry. Moreover, it influences the long-term outcome of the MPFL reconstructive surgery. A nonanatomic femoral fixation point should not be considered the cause of persistent pain and instability after MPFL reconstruction in all cases.

Level of evidence

III.

     

Lateral displacement,sulcus angle and trochlear angle are associated with early patellofemoral osteoarthritis following anterior cruciate ligament reconstruction

Purpose

Patellofemoral osteoarthritis (PFOA) occurs in approximately half of anterior cruciate ligament (ACL)-injured knees within 10–15 years of trauma. Risk factors for post-traumatic PFOA are poorly understood. Patellofemoral alignment and trochlear morphology may be associated with PFOA following ACL reconstruction (ACLR), and understanding these relationships, particularly early in the post-surgical time period, may guide effective early intervention strategies. In this study, patellofemoral alignment and trochlear morphology were investigated in relation to radiographic features of early PFOA 1-year post-ACLR.

Methods

Participants (aged 18–50 years) had undergone ACLR approximately 1 year prior to being assessed. Early PFOA was defined as presence of a definite patellofemoral osteophyte on lateral or skyline radiograph. Sagittal and axial plane alignment and trochlear morphology were estimated using MRI. Using logistic regression, the relationship between alignment or morphology and presence of osteophytes was evaluated.

Results

Of 111 participants [age 30 ± 8.5; 41 (37%) women], 19 (17%) had definite osteophytes, only two of whom had had patellofemoral chondral lesions noted intra-operatively. One measure of patellar alignment (bisect offset OR 1.1 [95% confidence interval 1.0, 1.2]) and two measures of trochlear morphology (sulcus angle OR 1.1 [1.0, 1.2], trochlear angle OR 1.2 [1.0, 1.5]) were associated with patellofemoral osteophytes.

Conclusions

Patellofemoral malalignment and/or altered trochlear morphology were associated with PFOA 1 year following ACLR compared to individuals post-ACLR without these features. Clarifying the role of alignment and morphology in post-traumatic PFOA may contribute to improving early intervention strategies aimed at secondary prevention.

Level of evidence

IV.

     

The inferomedial patellar protuberance and medial patellar ossicle in patellar instability

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.

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.

     

Lateral retinaculum plasty instead of lateral retinacular release with concomitant medial patellofemoral ligament reconstruction can achieve better results for patellar dislocation

Purpose

To elucidate the outcomes of lateral retinaculum plasty versus lateral retinacular release with concomitant medial patellofemoral ligament (MPFL) reconstruction.

Methods

In a prospective study, 59 patients treated at our institution from 2012 to 2014 were included. The 59 patients were randomly divided into two groups. Group I included 27 patients who underwent lateral retinacular release and MPFL reconstruction. Group II included 32 patients who underwent lateral retinaculum plasty and MPFL reconstruction. All patients were followed up for at least 2 years and all assessments were performed both pre- and post-operation. Clinical evaluation consisted of the Kujala score, patellar medial glide test, and patellar tilt angle, patellar lateral shift, and congruence angle, measured on CT scan.

Results

Significant improvement was seen after surgery in both groups. The group of lateral retinaculum plasty achieved better results than the group of lateral retinacular release. No statistically significant differences were found in lateral patellar shift (ns) or congruence angle (ns) between the groups. There were significant differences in Kujala score (P?<?0.05) patellar tilt angle (P?<?0.05), and patellar medial glide test (P?<?0.05) between the groups.

Conclusions

MPFL reconstruction with lateral retinaculum plasty yielded better results than MPFL with lateral retinacular release. Postoperatively, medial and lateral function were restored, and patellar tracking was normal. Lateral retinaculum plasty is a new method that reduces the complications of lateral retinacular release for patellar dislocation.

Level of evidence

II.

     

The effects of conventional and oval chainrings on patellofemoral loading during road cycling: an exploration using musculoskeletal simulation

Purpose

The aim of the current investigation was to utilize a musculoskeletal simulation approach to resolve muscle forces during the pedal cycle, to specifically examine the effects of chainring geometry on patellofemoral loading during cycling.

Methods

15 healthy male recreational cyclists rode a stationary cycle ergometer at a fixed cadence of 70 RPM in two chainring conditions (round and oval). Patellofemoral loading was explored using a musculoskeletal simulation and mathematical modeling approach. Differences between chainring conditions across the entire pedal cycle were examined using one-dimensional statistical parametric mapping, and patellofemoral force experienced per 20 km was explored using a paired samples t test.

Results

No significant (P > 0.05) differences in patellofemoral force or stress were found throughout the pedal cycle between chainring conditions. It was also shown that no significant (P > 0.05) differences in patellofemoral force per 20-km joint were evident (round 38,576.40 N/kg s and oval = 35,637.00 N/kg s).

Conclusions

The current analysis found no effects of chainring geometry, on the forces experienced by the patellofemoral joint during the pedal cycle.

     

Surgical treatment of patellofemoral instability using trochleoplasty or MPFL reconstruction: a systematic review

Purpose

Trochleoplasty and reconstruction of the medial patellofemoral ligament (MPFL) are among the most commonly performed surgical treatments in patients with patellofemoral instability. The primary purpose of the study was to perform a systematic literature review on trochleoplasty in the treatment of patients with patellofemoral instability. The secondary purpose was to compare the outcomes with those seen in patients treated after reconstruction of the MPFL.

Methods

A standardised search on search engines was performed. All observational and experimental studies dealing with trochleoplasty were then obtained and reviewed in a consensus meeting. Fifteen articles out of 1543 were included and analysed using the CASP appraisal scoring system. Twenty-five studies on MPFL reconstruction were obtained for comparison. The clinical and radiological outcomes were statistically analysed.

Results

Both treatment groups showed significant improvement in outcomes from pre- to post-operatively. The mean post-operative Kujala and the Lysholm scores significantly increased in both groups when compared to preoperatively (trochleoplasty group: Kujala 61.4–80.8 and Lysholm 55.5–78.5; MPFL group: Kujala 46.9–88.8 and Lysholm 59.9–91.1). Post-operatively a positive apprehension test was found in 20 and 8 % of the trochleoplasty and MPFL groups, respectively. No significant differences in redislocation (2 %) and subluxation (5–6 %) rates were found.

Conclusions

This systematic review showed that both trochleoplasty and MPFL reconstruction are able to deliver good clinical outcomes with stable patellofemoral joints.

Level of evidence

III.

     

Management of patellar problems in skeletally mature patients with nail–patella syndrome

Purpose

Nail–patella syndrome (NPS) or hereditary onychoosteodysplasia is a rare autosomal dominant disease, characterized by a tetrad of findings, which include fingernail abnormalities, hypoplasia of the patellae, radial head dislocation and prominent iliac horns. Most of the literature on the treatment of patellar problems in NPS concerns paediatric patients, and there is no standard treatment algorithm for adult patients.

Methods

We reviewed the charts of skeletally mature patients with NPS who presented to our clinic. We reviewed the presenting complaints, the physical examination findings and the radiographic imaging.

Results

We identified seven skeletally mature patients with NPS who presented with patellofemoral complaints. Their symptoms were instability, pain, or a combination of the two. Examination and imaging revealed a wide range of severity but included patellar instability and patellar arthritis. In our series, milder forms of the disease were treated with non-operative measures, but the majority of our patients required surgery including medial patellofemoral ligament reconstruction, tibial tuberosity transposition, patellofemoral and total knee arthroplasty. At midterm follow-up, most patients had good results.

Conclusion

Nail–patella syndrome has a wide range of presentations and severity in skeletally mature patients. Knee surgeons should be familiar with the spectrum of clinical presentation and the range of treatment options available in order to provide optimum treatment for patients with this disorder.

Level of evidence

IV.

     

Patellar tendon length during knee flexion of meniscal-bearing and rotating total knee arthroplasty implants

Purpose

The length of the patellar tendon after total knee arthroplasty (TKA) has most commonly been compared with preoperative measurements. However, there are no reports that discuss changes in the length of the patellar tendon during knee flexion after TKA. The purpose of this study was to evaluate changes in the length of the patellar tendon during knee flexion and to clarify the impact of changes in patellar tendon strain on the length of the patellar tendon and post-operative range of motion (ROM) after TKA.

Methods

Thirty-six patients undergoing sequential bilateral TKA for osteoarthritis were evaluated. Patients received a meniscal-bearing (MB) implant on one side and a rotating platform (RP) implant on the other and were followed for a median of 115 months (range 60–211 months). The lengths of the patellar tendon at maximum extension, 30°, 60°, 90° and maximum flexion were measured, and the post-operative ROM of both knees were assessed. The effects of implant design and the knee flexion angle on the length of the patellar tendon were analysed using a linear mixed-effects model. The relationship between patellar tendon strain and post-operative knee ROM was assessed using Pearson’s correlation coefficients.

Results

Post-operative clinical scores were similar for MB and RP implants. Neither the implant design nor the knee flexion angle significantly affected the length of the patellar tendon. The ROMs in the two designs at final follow-up were equivocal (114° in MB, 113° in RP). There was no correlation between patellar tendon strain and ROM in knees with either implant type.

Conclusions

Patellar tendon lengths after mobile-bearing TKA with implants that permitted different anteroposterior constraints were relatively constant at varying degrees of knee flexion. Differences in patellar tendon strain may not impact ROM. These results provide conclusive evidence that the quality of the patellar tendon may play a less important role in ROM after TKA.

Level of evidence

Therapeutic study, Level II.

     

Origin and insertion of the medial patellofemoral ligament: a systematic review of anatomy

Purpose

The medial patellofemoral ligament (MPFL) is the major medial soft-tissue stabiliser of the patella, originating from the medial femoral condyle and inserting onto the medial patella. The exact position reported in the literature varies. Understanding the true anatomical origin and insertion of the MPFL is critical to successful reconstruction. The purpose of this systematic review was to determine these locations.

Methods

A systematic search of published (AMED, CINAHL, MEDLINE, EMBASE, PubMed and Cochrane Library) and unpublished literature databases was conducted from their inception to the 3 February 2016. All papers investigating the anatomy of the MPFL were eligible. Methodological quality was assessed using a modified CASP tool. A narrative analysis approach was adopted to synthesise the findings.

Results

After screening and review of 2045 papers, a total of 67 studies investigating the relevant anatomy were included. From this, the origin appears to be from an area rather than (as previously reported) a single point on the medial femoral condyle. The weighted average length was 56 mm with an ‘hourglass’ shape, fanning out at both ligament ends.

Conclusion

The MPFL is an hourglass-shaped structure running from a triangular space between the adductor tubercle, medial femoral epicondyle and gastrocnemius tubercle and inserts onto the superomedial aspect of the patella. Awareness of anatomy is critical for assessment, anatomical repair and successful surgical patellar stabilisation.

Level of evidence

Systematic review of anatomical dissections and imaging studies, Level IV.

     

Clinical outcome after reconstruction of the medial patellofemoral ligament in patients with recurrent patella instability

Purpose

We present the clinical results of a large consecutive, prospective, single-clinic series of patients treated with medial patellofemoral ligament (MPFL) reconstruction for recurrent patellar instability.

Methods

The study included 224 patients undergoing MPFL reconstruction in a total of 240 knees between 2008 and 2011. Indication for surgery was two or more patellar dislocations and ADL limitations due to patella instability. Surgical procedure: A gracilis tendon autograft was fixed in drill holes in the medial edge of the patella and with screws at the femoral MPFL insertion point. Outcomes were evaluated with the Kujala Anterior Knee Pain Score and pain scores preoperatively and at follow-up (12–60 months). Furthermore, incidences of re-dislocations, subluxations and revision surgery were evaluated.

Results

The Kujala score improved from 62.5 (17) to 80.4 (18) (p < 0.001) at the 1-year follow-up. Pain during activity improved from 3.2 (2.6) to 1.3 (2.7) at 1 year (p < 0.001). The revision rate was 2.8 %. Some degree of pain at the medial femoral condyle was seen in 30 % of the patients. The reconstruction was supplemented with a tibial tuberosity osteotomy in 23 % of cases. The outcome for these patients did not differ from that of patients with isolated MPFL reconstruction. Female gender BMI >30, age >30 years and grade 3–4 cartilage injury predisposed a poor subjective outcome.

Conclusions

The present study is the largest MPFL reconstruction patient material reported to date. MPFL reconstruction with a gracilis tendon autograft consistently normalised the patella stability and improved knee function. Moderate medial pain was seen. Age above 30, obesity, cartilage injury and female gender are predictors of a poor subjective outcome.

Level of evidence

Level IV.

     

Tibial tubercle–trochlear groove distance and angle are higher in children with patellar instability

Purpose

The purpose of this study was to assess the variations in tibial tubercle–trochlear groove distance and angle as a function of age and gender in a population of children without patellar instability (PI) compared with those with PI.

Methods

A retrospective review of 869 children’s knee MRIs, ages 5 to 15 years, were evaluated using a control group (792 children) without evidence of PI and a group with PI (77 children). Tibial tubercle–trochlear groove distance (TT–TGd) and angle (TT–TGa) were measured twice by two readers to assess intra- and inter-observer reliability and compared between PI and control groups. In both groups, functions of age and gender on TT–TGd and TT–TGa values were evaluated.

Results

Both TT–TGd and TT–TGa measurements showed excellent intra- and inter-observer reliability. The mean TT–TGd for the PI group was 17.2 mm (SD 6.6) and significantly higher than the mean TT–TGd for the control group (10.4 SD 3.8 mm, P?=?0.001). The mean TT–TGa for the PI was 20.8° (SD 8.3°), which was also significantly higher than the mean TT–TGa for the control group (12.5° SD 4.6°, P?<?0.001). Control group revealed a positive correlation between age and TT–TGd measurements (r?=?0.243, P?<?0.001). The mean TT–TGa for girls (13.3° SD 4.7°) was higher than the mean TT–TGa for boys (11.9° SD 4.4°) in the control group (P?<?0.001).

Conclusion

TT–TGa and TT–TGd are reliable and can be used for the evaluation of the extansor mechanism alignment in children with and without PI. However, it must be considered that TT–TGd is increasing in growing patients. Soft-tissue procedures may be prone to failure, since bony procedures for patellar alignment cannot be done until skeletal maturity.

Level of evidence

III.