Patellar Groove Replacement in Patellar Luxation with Severe Femoro-Patellar Osteoarthritis

Clinical Communication 124

Patellar groove replacement in patellar luxation with severe femoro-patellar osteoarthritis

Z. Dokic1; D. Lorinson1; J. P. Weigel2; A. Vezzoni3 1Chirurgische Überweisungspraxis, Vösendorf, Austria; 2College of Veterinary Medicine, Department of Small Animal Clinical Sciences, University of Tennessee, Knoxville, TN, USA; 3Clinica Veterinaria Vezzoni srl, Cremona, Italy

a Keywords months postoperatively and at longer term placement prosthesis in cases of patellar Dog, patellar luxation, partial stifle joint when available. luxation with severe femoro-patellar os- prosthesis Results: Thirty-five cases of patellar luxation teoarthritis. For this study, the null hypoth- ranging from grades II to IV were included. esis states that patellar groove replacement Summary Eleven of these cases had prior surgical inter- prosthesis will have no effect on the lame- Objective: To report a novel method of treat- ventions which failed to stabilize the patella. ness associated with femoro-patellar ing femoro-patellar instability in association Fourteen dogs required additional surgical osteoarthritis. with severe femoro-patellar osteoarthritis, by procedures in conjunction with patellar substituting the femoral trochlear with a pa- groove replacement. Complications occurred tellar groove replacement prosthesis. in six patients, of which three required revi- Materials and methods Study design: Retrospective case series. sion. Complete resolution of subjectively- Methods: Preoperative lameness was scored assessed lameness was evident in 24/35 Medical records from two different institu- from 0–4, and radiographic studies including cases by the third month and in another tions (Chirurgische Überweisungspraxis, standard positions for patellar luxation were seven of 35 patients on the longer term Austria; Clinica Veterinaria Vezzoni srl, obtained for evidence of malalignment and re-evaluations. Italy) were reviewed to identify dogs af- femoro-patellar osteoarthritis. Cases with or Clinical significance: Use of a patellar fected by persistent patellar luxation and without previous surgeries were included. groove replacement prosthesis has the po- treated by patellar groove replacement. The The size of trochlear implant was determined tential to decrease the lameness associated inclusion criteria of the study were as fol- by transparent templates and confirmed with severe femoro-patellar arthritis, to im- lows: dogs affected with chronic medial or intra-operatively with trials. Radiographic improve patellar stability, and to correct the lateral patellar luxation, with or without ages, together with clinical examinations, alignment of the extensor mechanism. cranial cruciate ligament injury, with intra- were reviewed immediately and at three operative assessment of severe femoro- patellar osteoarthritis which would impede efficient trochleoplasty, and a minimum Correspondence to: Vet Comp Orthop Traumatol 2015; 28: 124–130 clinical and radiographic follow-up time Aldo Vezzoni http://dx.doi.org/10.3415/VCOT-14-07-0106 period of three months. Exclusion criteria Clinica Veterinaria Vezzoni srl Received: July 13, 2014 included severe femoro-tibial osteoarthritis V. Massarotti, 24 Accepted: December 10, 2014 Cremona 261000 Epub ahead of print: February 4, 2015 requiring total knee replacement prosthe- Italy sis. Phone: +39 0372 23451 E-mail: [email protected] Preoperative clinical assessment Information obtained from the medical records included: date of presentation, date Introduction ever the reported complication rate is as of surgery, signalment, clinical history, di- high as 29% including a recurrence rate up rection of patellar luxation (medial or lat- Chronic instability and erosion of the to 15% (5, 6). Additionally, osteochondral eral), grade of patellar luxation according femoro-patellar joint surfaces result in trocheoplasty is not feasible when osteo- to the Putnam scale of grade I to IV, pre- lameness and progressive osteoarthritis (1, phytes and cartilage erosion have severely vious surgical procedures, visual gait analy- 2). Osteochondral trochleoplasties have damaged the trochlear groove (▶ Figure 1). sis by the surgeons (DL, AV) for the lame- been used to deepen the trochlear groove The objective of this pilot study was to in- to provide patellar stability, with or without vestigate the benefits of replacing the additional surgical procedures (3, 4). How- trochlear groove with a patellar groove re- a KYON AG, Zurich, Switzerland

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ness score (7). Lameness was assessed subjectively at the walk and trot and graded from 0 to 4 using the following scale: 0 = no lameness; 1 = mild, intermittent weight- bearing lameness; 2 = persistent moderate weight-bearing lameness; 3 = persistent severe weight-bearing lameness, with or without intermittent non-weight bearing; and 4 = persistent non-weight-bearing lameness (▶ Appendix Table 1: Available online at www.vcot-online.com).

Implant design Figure 1 Intra-operative appearance of the femoral trochlea of case 19 (A), case 5 (B), and case 21 (C). The patellar groove replacement prosthesis was a two-component implant comprised of a base plate and a trochlear prosthesis (▶ Figure 2). The base plate was perforated grade 4 titanium. To promote osseous integration it was coated with a glow discharge anodisation with incorporation of calcium phosphateb. The trochlear prosthesis was made of grade 5 titanium (Ti6Al4V). It was anatomically shaped on the upper face, highly polished, and treated with amor- phous diamond-like carbon coatingc to Figure 2 Two component implants for patellar groove replacement. Image shows the base plate for provide a very low coefficient of friction, fixation to the condyle and the trochlear prosthesis. Image courtesy of KYON AG (PGR Brochure). scratch resistant surface. The base plate was provided with three conical holes matched view of the femur plus the caudo-cranial kg) and anaesthesia was induced with pro- to the conical feet of the trochlear prosthe- view of the tibia, instead of the standard pofolf (1-6 mg/kg) and maintained with sis and was secured to the bone by either medio-lateral view of both femur and tibia, isoflurane in oxygen. Cefazolin natricumg two bone screws (1.5 mm, titanium alloy were used to document skeletal alignment. (22 mg/kg IV) was administered at the for the smallest four sizes of the prosthesis, From the medio-lateral radiographs, the time of induction and repeated after 90 or by four bone screws (2.4 mm, titanium size of the trochlear implant was deter- minutes. Dogs were positioned in dorsal alloy) for the larger sizes. The feet of the mined using a transparent template over recumbency and aseptically prepared for trochlear prosthesis were aligned with the the radiograph (▶ Figure 3), such that the surgery. Either a medial parapatellar ap- receiving holes of the base plate and were base of the patellar groove replacement im- proach for medial patellar luxation or a lat- firmly seated by light tapping by hammer to plant was aligned to a line from the point of eral parapatellar approach for lateral patel- achieve a press-fit locking. A gap of about 1 the origin of the long digital extensor to the lar luxation was performed (8). After re- mm remained between the upper compo- most proximal edge of the trochlea. flection of the patella, an osteotomy of the nent and the base plate to insure the coni- trochlea, parallel to the frontal plane was cally fitted feet fully engaged the base plate. Surgical technique performed with an oscillating saw starting distally at the level of the origin of the ten- Radiographic study and planning All surgical procedures were performed by don of the long digital extensor muscle, two board certified surgeons (AV and DL). ending proximally at the proximal end of Preoperative radiographs were obtained to Preoperatively, each dog was evaluated for the trochlea. In the case of femoral torsion, document the patellar instability, patellar any haematological or serum biochemical the osteotomy was slightly tilted medial or location, and to assess extensor alignment, alterations. Animals were pre-medicated lateral to correct for torsion, keeping 25° to and trochlear depth. The skyline view was with morphine hydrochlorided (0.2 mg/kg) 35° as a normal reference for femoral neck used to document trochlear shape and and medetomidine hydrochloridee (2 mcg/ anteversion angle (9). In medial patellar lu- depth. The cranio-caudal view and axial

d Morphin: HBM Pharma, Martin, Slovakia; Morfina f Propofol-Lipuro 1%: B Braun, Melsungen, cloridrato: Molteni, Scandicci (FI), Italy Germany; Propovet, Esteve, Italy b Biocer®: Innosurf, Châtel-St-Denis, Switzerland e Domitor: Orion Pharma, Espoo, Finland g Cefazolin: Sandos, Kundl, Austria; Cefazolina: c Ionbond, Olten, Switzerland Teva, Assago (MI), Italy

Vet Comp Orthop Traumatol 2/2015 © Schattauer 2015

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and stability of the reduction was assessed with flexion and extension of the stifle. The necessary adjustments made included insertion of a larger or smaller trial prosthesis or removal of an additional slice of bone. In addition, a proper fit of the patella inside the prosthetic trial trochlea was verified. Adjustments were made by finding the best medio-lateral and proximo-distal position of the trial prosthesis to stabilize the patella. Tibial tuberosity transposition was not generally required, since the patella could be realigned by simply moving the trochlear prosthesis medially or laterally in the frontal plane. Moreover, in cases of medial patellar luxation, the prosthetic groove could be fixed more proximally to counteract the tendency of medial luxation occurring with extension of the stifle, while in cases of lateral patellar luxation it could be A B fixed more distally to counteract the ten- Figure 3 Transparent template placed over the radiograph to plan the size of the implant. dency of lateral luxation happening during stifle flexion (11). Femoral varus or valgus was partially compensated by rotating the prosthesis in the frontal plane. Once the xation, the anteversion of the femoral neck flat rasp, to be as flat and uniform as possi- preferred position of the trial prosthesis is reduced, and the femoral condyle has an ble for fixation of the base plate. A trial was found, the bone was gently marked external torsion, thus the osteotomy was prosthesis, available in 10 different sizes, with an osteotome so that the base plate of tilted toward medial in the frontal plane to was positioned on the osteotomy surface the final patellar groove replacement pros- compensate for the axial deformity (10). In (▶ Figure 4). The size was correct when the thesis could be fixed in the same position cases of lateral patellar luxation, with in- proximal and distal borders of the trial (▶ Figure 5, ▶ Figure 6). The base plate creased femoral neck anteversion and in- prosthesis matched with the corresponding was stabilized to the bone with two to four ternal femoral torsion, the osteotomy was edges of the osteotomy. With the trial pros- titanium cortical screws, depending on the tilted toward lateral. If necessary, the sur- thesis in position on the femur, the patella size of the implant. The final prosthesis was face of the osteotomy was prepared with a was reduced and the tightness or looseness press-fitted to the base plate by aligning the three conical pegs of the prosthesis to the corresponding holes in the base plate and gently tapping the prosthesis with a Teflon hammer. The patella was then reduced and tested again in flexion and extension. Some patelloplasty was performed if required by trimming the lateral and medial borders of the patella if it was too wide or flat to seat properly inside the trochlea. Capsulor- raphy with imbrication of the opposite side to the luxation was performed, and leaving the capsule open on the same side of the luxation in the grade IV cases. Subcutis and skin were routinely sutured completing the surgical procedure.

Additional surgical procedures

Figure 4 Trial prosthesis moved medial or lateral in the coronal plane in a plastic bone model to find When the underlying limb deformities the best alignment with the tibial tuberosity. Image courtesy of KYON AG (PGR Brochure). were too severe and it was not possible to

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realign the quadriceps mechanism with patellar groove replacement alone, or when cruciate ligament failure was concomitant, additional surgical procedures were performed in combination with patellar groove replacement including tibial tuberosity transposition, distal femoral osteotomy, proximal tibial osteotomy, tibial plateau levelling osteotomy or tibial tuberosity advancement (▶ Appendix Table 1: Avail- able online at www.vcot-online.com).

Postoperative patient evaluation and management Postoperative cranio-caudal and medio- lateral radiographs of the full femur with Figure 5 Fixation of the base plate and insertion of the trochlear prosthesis in a plastic bone model. the stifle positioned in flexion and exten- Image courtesy of KYON AG (PGR Brochure). sion were obtained to evaluate the osteotomy site, and to confirm the patellar reduction and prosthesis position. When femoral torsion was compensated with a tilted os- alteration of bone interface with the pros- determine statistical significance. Com- teotomy, the axial radiographic view was thesis, and progression of osteoarthritis. mercially available software was used for also taken. A modified Robert Jones ban- Clinical evaluation assessed the status of the statistical analysisj. dage was applied for the first 24 – 48 hours extensor realignment, passive range-of- postoperatively. Pain was controlled during motion with or without signs of pain, the first two days with administration of muscle tone, and strength. Gait evaluation Results morphine hydrochloride (0.2 mg/kg SC q 6 assessed the absence or the degree of lame- Preoperative clinical findings and hr) and meloxicamh (0.1 mg/kg SC q 24 hr) ness. This analysis was divided into a short- for five days. Cephadroxili (20 mg/kg PO q term follow-up (3 months) and into a long- surgical details 12 hr) was administered for five days. Post- term follow-up (6 months and over) when Findings are summarized in ▶ Appendix operative exercise restriction to leash walk- available (▶ Figure 7). Table 1 (Available online at www.vcot-on ing was enforced for two months, which line.com). Of the 35 cases that met the in- was followed by a gradual increase in the Statistical analysis clusion criteria, 16 were males, one was a following month up to normal levels of ac- neutered male, 12 were females, and six tivity. When indicated in chronic condi- A paired t-test or non-parametric signed were female-spayed. Of the 35 cases, medi- tions with reduced range-of-motion of the rank test was used to assess the difference al patellar luxation was present in 29, of affected stifle, physiotherapy was recom- in lameness scores. The test statistic of which 22 were grade III luxation and six mended. Shapiro-Wilk was used to compare con- tinuous measurements to a normal dis- Follow-up tribution. A p-value of <0.05 was used to j SAS version 9.4: SAS Institute, Cary, NC, USA During the follow-up period, outcome assessment was focused on clinical and radiographic examination at three months after surgery, and more frequently and at longer term when indicated or possible. Radiographic assessments included stability and position of the patellar groove replacement implant, patellar reduction, any

h Metacam: Boehringer Ingelheim Vetmedica, Brack- nell, UK Figure 6 Case 9: Osteotomy of the degenerated trochlea, fixation of the base plate and insertion of i Cefa Cure: Intervet Int, Boxmeer, The Netherlands the trochlear prosthesis.

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Figure 7 Case 6: Preoperative (Pre-op), postoperative (Post-op) and three years follow-up (FU) radiographs.

were a grade IV. Lateral patellar luxation scores between the short-term and long- after surgery included excision of 3–4 mm was present in six cases, of which one was a term follow-up periods were also signifi- of excess bone over the extensor fossa and grade II luxation and five were a grade IV. cant (p <0.0156) indicating a continued of redundant fibrous tissue from the proxi- The age ranged from eight to 125 months improvement beyond three months follow- mal border of the patella, which led to with a mean of 54.5 months. Body weight ing patellar groove replacement. The null complete improvement at three months. A ranged from 1.5 – 97.5 kg with a mean of hypothesis was rejected with these results, large breed dog (case 20) experienced 21.9 kg. All 35 cases had short-term (3 confirming a positive clinical effect with sudden lameness four months after surgery months) follow-up, whereas 33/35 had a the patellar groove replacement procedure. due to dislodgement of the prosthesis. The long-term follow-up (6 to 56 months). The Not all cases had patellar groove re- case was successfully revised with re-fitting median time for long-term follow-up was placement surgery alone as 14 patients of a replacement prosthetic trochlea in- 12 months and the mean 19 months. required additional surgical treatment including the base which had been altered by The sizes of prosthesis used in these cluding tibial tuberosity transposition (n = friction with the loose implant. The dog cases were as follows: 1 (n = 3), 2 (n = 3), 3 5), tibial plateau levelling osteotomy (n = had regained normal function by eight (n = 4), 4 (n = 5), 5 (n = 1), 6 (n = 2), 7 (n = 4), tibial tuberosity advancement (n = 1), months following revision. A medium size 8), 8 (n = 2), 9 (n = 5), 10 (n = 2). distal femoral osteotomy (n = 3), and dog (case 22) had a recurrence of medial proximal tibial osteotomy (n = 3), and a patellar luxation one month after surgery Outcome lateral fabellar-tibial suture in one case. requiring limb alignment because of ex- However in 21 cases where the underlying cessive distal femoral varus (anatomical Findings are summarized in ▶ Appendix limb deformities were less severe, patellar lateral distal femoral angle 107°) and exter- Table 1 (Available online at www.vcot- groove replacement was the only procedure nal femoral torsion (femoral anterversion online.com). All 35 cases were lame prior done. angle 15°). Distal femoral osteotomy with a to surgery with lameness scores ranging final anatomic lateral distal femoral angle from 2 – 4 (median score of 3). Three Complications of 95° and femoral anteversion angle of 30° months following surgery, all cases im- was performed. Patellar reduction was con- proved with lameness scores ranging from Complications were observed in six cases, firmed 11 months following the additional 0 to 1 (mean score of 0.3). Specifically of which three required surgical revision. osteotomies. At three months following the 24/35 cases were not lame at three months In one unrevised case (case 2), an oversized patellar groove replacement procedure, while 11/35 cases were still lame but with a implant resulted in capsule tension and three dogs (cases 3, 5, and 19) that had lesser score compared to the preoperative thickening. Two others were a Chihuahua chronic patellar luxation and severe preop- lameness. The long-term evaluation deter- (case 4) and a Yorkshire Terrier (case 33) erative osteoarthritis had some progression mined that 23 of the 33 with a lameness with medial tilting of the patella inside the of the arthritis evident on the follow-up score 0 at three months remained un- patellar groove replacement prosthesis radiographs. In the remaining 32 cases pro- changed in longer term evaluation, seven which nevertheless did not cause lameness gression of osteoarthritis was not observed. improved from a lameness score of 1 to 0 or discomfort on stifle manipulation. Of and three remained with a score of 1. Dif- the three cases requiring surgical revision, ferences in lameness scores between pre- a mongrel (case 7) demonstrated painful Discussion surgery and short-term follow-up and impingement during range-of-motion in long-term follow-up were significant (p the third and fourth week after surgery, The patellar groove replacement procedure <0.0001) indicating an improvement in where the patella slipped over the distal has the potential to restore function to dogs function following patellar groove replace- end of the prosthesis creating a “clunk” with severe femoro-patellar arthritis. The ment surgery. Differences in lameness sensation. Revision performed one month patellar groove replacement also provides

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for improved patellar coverage and align- tellar luxation. Case 22 demonstrated the when patellar alignment was not addressed ment of the extensor mechanism with or requirement for additional corrective fe- with specific osteotomies if required. without tibial tuberosity transposition or moral osteotomy for a successful restora- The incidence of complications de- other corrective osteotomy. In our opinion, tion of function. In this case, a recurrence creased with an increasing number of balanced tracking of the patella is more of patellar luxation occurred after patellar cases, suggesting that surgeon experience likely to result with the patellar groove re- groove replacement because the femoral played a role in the complication rate. Ex- placement procedure than with plain or re- deformity and subsequent malalignment perience improved the selection of the ap- cession trochleoplasty because the tall were overlooked. However, where the propriate size of implant preventing over- ridges and smooth contours of the prosthe- underlying limb deformities were less se- sizing. Proper positioning of the implant sis allow for more deep gliding of the patel- vere, fixation of the patellar groove replace- also improved with the experience of the la. The smooth surface of the prosthesis ment prosthesis in line with the quadriceps surgeon. also provides a low friction surface for mechanism allowed proper realignment A primary limitation of this study was smooth gliding of the patella, reducing tis- without further surgical procedures. Also, the survey basis as the principal assessment sue damage and inflammation. Fur- the capability of fixing the patellar groove of outcome. Surveys of the surgeons were thermore, moderate varus-valgus and ex- replacement prosthesis slightly more pro- done with a base standardized system to ternal-internal torsion of the femur can be ximally in the case of medial patellar lu- improve reliability. However, the authors compensated by setting the prosthesis in a xation or more distally in the case of lateral recognize the inherent bias that exists in calculated angle of inclination in the front- patellar luxation than the original trochlea, such data and a repeated study with im- al plane. allows treatment of patella alta or baja. In proved design including a control group Reduction of lameness assessed by clini- this current series of cases, patellar groove and an evaluation by a clinician who is cal survey suggests a prompt and notable replacement was performed concurrently blinded to the operative procedure would postoperative recovery. Lameness scores with other surgical procedures in 14 cases. be indicated. dropped to 0 during the first few weeks in In eight of these cases, the additional sur- Nevertheless, this study has shown that 24 dogs, and in further seven cases in the gery was done to correct severe femoral or the patellar groove replacement implant is longer term. The three dogs with persistent tibial deformities or both. In the other six well tolerated without adverse reactions. grade 1 lameness in the long-term also had cases, patellar groove replacement was per- The patellar groove replacement procedure concurrent cruciate ligament rupture with formed with procedures designed to ad- has the potential to improve function in the chronic patellar luxation, which could dress cranial cruciate deficiency. case of severe femoro-patellar osteoarthri- explain that outcome. Multiple preoper- Bone ingrowth and absence of any ad- tis due to chronic patellar luxation, and it ative and adjunctive surgical procedures verse bone reaction are characteristics of has the potential to improve the alignment may increase the likelihood of residual medical grade titanium (12, 13). The patel- of the extensor mechanism in the case of morbidity. The mild progression of os- lar groove replacement prosthesis is a tita- moderate malalignment and keeping the teoarthritis observed in three cases with nium implant designed for bone ingrowth patella permanently reduced. More exten- chronic luxation and severe preoperative and minimal tissue reaction. Aseptic loo- sive clinical studies with confirmed statisti- osteoarthritis did not correlate with clinical sening was not recognized in this series of cal outcomes will be essential in establish- performance. clinical cases, suggesting appropriate bone ing the role of the patellar groove replace- Oversizing the prosthesis could lead to integration with the base plate. Actual in- ment implant in the treatment of femoro- soft tissue impingement suggesting that growth cannot be confirmed by radio- patellar abnormalities in the dog. More- proper planning and intra-operative testing graphic imaging and clinical performance over, computed tomographic evaluation of with a trial prosthesis is necessary to find alone, but considering the long-term stabil- the skeletal abnormalities causing patellar the right size for each patient. Two dogs ity and function of the implant evaluated in luxation could provide more precise (cases 4 and 33) had medial patellar tilt vis- the 21 cases with a minimum of one year measurements for surgical planning com- ible on the skyline radiographic views des- follow-up indicates successful bone tissue pared to plain radiographs. pite a more medial implant position, prob- ingrowth and absence of inflammatory tis- ably because of a proportionally wider pa- sue reaction. Acknowledgements tellar groove replacement prosthesis size to Case 20 had a dislocation of the troch- patellar size and a persistent malalignment lear prosthesis which may have been due to The authors would like to thank B. W. of the extensor mechanism requiring tibial an incomplete press fit at the time of im- Rohrbach from the department of Stat- tuberosity transposition. plantation. Loosening of the base plate istics/Epidemiology at the University of While the patellar groove replacement from the underlying bone was not evident Tennessee, College of Veterinary Medicine, prosthesis has the potential to improve in this case; nevertheless dislodgment of Knoxville, TN, USA, for the statistical function in case of severe femoro-patellar the prosthesis constitutes an incidence of evaluation. arthritis, it cannot be expected to compen- implant loosening. Dislodgment of the sate alone for marked bone deformities trochlear prosthesis could potentially also occurring in cases of grade III and IV pa- occur because of patellar mal-tracking

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