Prof. Dr. Cristea Stefan

Ortopedie și traumatologie

Bucuresti, Hyperclinica Medlife - Central

PATELLAR RETENTION VERSUS PATELLAR RESURFACING DURING TKA – A PROSPECTIVE, RANDOMIZED STUDY

PATELLAR RETENTION VERSUS PATELLAR RESURFACING DURING TKA – A PROSPECTIVE, RANDOMIZED STUDY

Cristea St., Ciocarlan S., Predescu V., Prundeanu A., Georgeanu V., Groseanu Fl., Atasiei T., Panait Ghe.
Clinic of Orthopaedic and Trauma Surgery, St. Pantelimon Hospital, Bucharest, Romania
Abstract

Introduction: Existing data in the literature is supporting either patellar retention or patellar resurfacing during primary TKA. There is no clear answer for the question in which cases the patella should be retained or resurfaced during primary TKA.
Materials and Methods: In this prospective study 2 groups of patients with a mean follow up of 34 months after TKA were compared. 83 patients (98 TKA) were implanted with a TKA with patellar retention (group 1) while 93 TKA (86 patients) were done including a patellar resurfacing (group 2). The patients were randomized according to the year of birth. The Scorpio Stryker was implanted. A dome shaped patellar prosthesis with 3 pegs was used for patellar resurfacing. Clinical Outcomes were based on the knee society score parameters, anterior knee pain, patient satisfaction, feeling of instability, step test while component position and limb alignment were measured by standard radiographs.
Results: No statistical differences between both groups with regard to post-operative anterior knee pain and knee society score were found. We found no preoperative predictor factors for the development of post-operative anterior knee pain for each group and both together. Patellar mal-tracking was worse in group 2 than in the patellar retention group (3 cases with patellar subluxation in group 2 versus 2 cases in group 1).
Conclusion: According to the not significant differences for the clinical outcomes between group 1 and 2 we routinely retain the patella. Patellar resurfacing is done only in selective cases.
Total knee replacement is a complex procedure, and the patellar resurfacing could complicate more the evolution of this complex procedure.
Key words: Total knee arthroplasty (TKA), patella, resurfacing
Résumé
Introduction: Les données existantes dans la littérature sont incertes pour ce suget. Il n'y a pas de réponse claire à la question, dans quels cas la patella devrait être conservé ou réapparurent pendant PTG primaire.
Matériel et méthodes: dans cette étude prospective 2 groupes de patients avec un suivi moyen des 34 mois après PTG ont été comparés. 83 patients (98 PTG) ont été implantés avec un PTG avec conservation patellaire (groupe 1) tandis que 93 PTG (86 patients) ont été effectués, y compris un patellaire réfection du revêtement de (groupe 2). Les patients étaient randomisés en fonction de l'année de naissance. Le Stryker Scorpio a été implanté. Un dôme en forme de prothèse patellaire avec 3 chevilles a été utilisé pour le resurfaçage rotulien.
Résultats cliniques étaient basés sur le genou société score paramètres, la douleur antérieur du genou, la satisfaction des patient, sentiment d'instabilité, étape test tandis que la position du composant et l'alignement de membre ont été mesurés par radiographies standard.
Aucune différence statistique entre les deux groupes au regard de douleur postopératoire genou antérieur et genou société score a été trouvés. Aucun facteur prédictif préopératoire pour le développement de la douleur postopératoire genou antérieur pour chaque groupe et les deux ensembles nous n’avons pas trouvé. La subluxation patellaire, le maltracking était pire dans le groupe 2 que dans le groupe de nonresufaçage patellaire (3 cas avec subluxation patellaire dans le groupe 2 contre 2 cas dans le groupe 1).
Conclusion : selon aux différences non significatives pour les résultats cliniques entre le groupe 1 et 2 nous régulièrement conservons le patella. Le revêtement patellaire s'effectue uniquement dans les cas sélectifs. La prothèse totale de genou est une procédure complexe, et la réfection du revêtement de patella pourrait compliquer davantage les évolutions de cette procédure complexe.
Mot clee: prothese totale de genou PTG, patella, le resurfaçage rotulien

Introduction: Existing data in the literature is supporting either patellar retention or patellar resurfacing during primary TKA. There is no clear answer for the question in which cases the patella should be retained or resurfaced during primary TKA.
Materials and Methods: On these circumstances in “Saint PANTELIMON” Hospital, Bucharest from 2006 till 2010 we operated 169 patients with 191 total knee prosthesis. Our prospective study involve 2 groups of patients with a mean follow up of 34 months after TKA were compared. 83 patients (98 TKA) were implanted with a TKA with patellar retention (group 1) while 93 TKA (86 patients) were done including a patellar resurfacing (group 2). The patients were randomized according to the year of birth. The Scorpio Stryker was implanted. Dome shaped patellar prosthesis with 3 pegs was used for patellar resurfacing. Clinical Outcomes were based on the knee society score parameters - IKSS score, anterior knee pain, patient satisfaction, feeling of instability, step test while component position and limb alignment were measured by standard radiographs.

Fig.Nr.1 2 GROUPS OF PATIENTS : PATELlAR CONSERVATION – 83 PATIENTS / 98 TKA and PATELLAR RESURFACING– 86 PATIENTS / 93 TKA
Results and Discutions:
The causes of TKA failure are multiple: defixation of components, prosthetic instability, sepsis, components fracture, articular stiffness, periprosthetic fractures, interruption of extensor mechanism. But most frequently they are due to the patella itself (4 – 50%), namely: anterior pain, maltracking, instability (subluxation, or dislocation), necrosis, fracture, interruption of external mechanism, polyetilene wear, defixation of patellar component, impingement - fig. Nr.2.

Fig. Nr. 2 Causes of TKA failure – patella Fig.Nr.3 biomechanic of femuropatellar articulation [1-4]
The biomechanic considerations of femuro-patelllar articulation. During knee flexion the increasing force vector is proportional with the increasing cvadricipitale force. At 9 – 120 of knee flexion, practically on extension the force vector is 0,5 Gc, on climbing stairs the force increase at 3,3 Gc, but in maximal flexion 1300 the force vector is 7,8 Gc – fig.Nr.3. Therefore during knee flexion, the articular contact pressure increases, and the pressure forces are equally distributed for a certain flexion degree – fig.Nr. 4 [1,2]

Fig. Nr. 4 Articular pression in normal knee [1-4] Fig.Nr.5 Articular pression in TKA on femuro-patellar [1-4]

Fig. Nr. 6Various types of patella button [3-4] Fig.Nr.7 Articular pression in TKA on femuro-patellar [3-4]

Fig. Nr. 8 Restoration of the patellar thickness [3-4] Fig.Nr.9 The patella placement in TKA on femuro-patellar [3-4]

Fig. Nr. 10 Restoration of external rotation of femoral component [3-4] Fig.Nr.11The patella placement in TKA [3-4]

Fig. Nr. 12 Restoration of tibial placement component [3-4] Fig.Nr.13 Reproductibility of articular interline in TKA [3-4]

Fig. Nr. 14 the correct closing of the internal retinaculum [3,4] Fig.Nr.15 Radiological evaluation in TKA [3,4]

Fig.Nr.16 C.T. evaluation in TKA [3,4]
In total knee arthroplasty the biomechanics are completely modified, with or without patellar button, [5] Fig. Nr.5 In TKA with patellar button, the patella realizes a complex movement : gliding, rolling and rotation. So the biomechanical factors are variable with the prosthetic design and also with surgical technique – Fig 6 – 14.
The prosthetic design is variable with femoral component, proximal extension of femoral flanche, notch geometry – distal extension, oblicity and notch deepness and inclination.
On the surgical technique, the restorations of patellar thickness is difficult. Excessive bone resection has fracture risk, in contrary the minus resection will increase the pressure in femuro-patellar articulation and there will be more pain. The placement of the patellar button must not disturb the patellar tracking during the knee flexion. The maltracking is due to an oblique cutting of the patella or to a lateral placement, the best restore is the medial and superior placement of the patellar button. Smaller patella is better than bigger. The patellar displacement can be secondary to an mal rotation of the femoral component. For that we must rotate externally 30 from posterior condilar plan, we must respect biepicondilar plan and the Whiteside line. We must respect the Q angle, maximal 70 of valgus, the lateralization of the femoral component. Also the dimension of femoral component in antero-posterior, can influence the pressure on femuro-patellar articulation.
The patellar displacement can be also secondary to a wrong rotation of the tibial component, external rotation or lateralization of the tibial prosthesis. So the restore of the articular interline is very important, in patella baja will increase the pression and the mobility will diminish. The ligamentary balance is also very important. Finally the correct closing of the internal retinaculum is important, for that “no thumb test” by watching patellar gliding will be fine.
The imagistic evaluations include x-rays: frontal, lateral, and axial view. Fig15 or C.T. exam.fig 16.
Existing data on literature regarding this subject are not certain. There is no consensus regarding when to keep or to resurface the patella. There are a few papers regarding this particular subject based on bilateral knee prosthesis. In one of them Enis, CORR in 1993 conclude the patients are greater pain on knee with patellar conservation and the muscular force greater on the resurfaced knee. In contrary in others studies on 13 bilateral TKA Levitsky & Scott, COOR in 1999 conclude similar results in 6/13 (46%) and in others 6/13 (46%) the better results for conservation, in only 1/13 (7,7%) – better results for resurfacing . Similar Bourne& Rorabek in J. Arthroplasty 2003, analyzing 100 cases on 10 years conclude that in first 2 years better results for conservation but at long terme results can be modified [6].
In meta-analysis on 15 articles based on 1496 TKA in which 48,6% are resurfated and lesser anterior pain with better functional score - Parvizi J. Arthroplasty, 2004 [7].
In contrary on 10 articles based on 1223 TKA - Pakos, JBJS, 2005,[8] lesser incidence of anterior pain (13, 8%) for cases with patella conservation. Similar Nizard, Sedel, CORR, 2005 – analyzing 12 articles conclude that :1. patellar revision 2,3% (PR) / 6,5% (PC), (p:0.007) 2. anterior pain : 7,6% (PC) / 22,3% (PR), (p: 005) and 3. pain on climbing stairs: 12,7% (PC) / 26,4% (PR), (p:0.01) [9].
No statistical differences between both groups with regard to post-operative anterior knee pain and knee society score were found. We found no preoperative predictor factors for the development of post-operative anterior knee pain for each group and both together. Patellar mal-tracking was worse in group 2 than in the patellar retention group (3 cases with patellar subluxation in group 2 versus 2 cases in group 1). Fig .17

Fig.Nr.17 Clinical results [3,4]
Finally our indications for conservation the patella in TKA are: minimal arthrosis in femuro-patellar, small patella (hipoplasic) or too thin, young patients actives, congruent patellar traking verified during surgery .
Our indications for resurfacing the patella in TKA are: advanced femuro-patellar arthrosis (outerbridge iv), older patients, obesity, inflamatory arthropaties, patellar subluxations / patellar maltraking and on women which is a relative indication.
Conclusion:
The biomecanics of articulation with patellar resurfacing is completely changed. The existing data in literature are uncertain.
The patellar resurfacing is a difficult surgery task and can lead to suplimentary complications.
Although the femuro-patellar artrhroplasty remain a valable procedure.
Patellar revision (isolated patellar resurfacing ) is difficult, the results are worse than primary artrhroplasty . There are specific indications for resurfacing or conservation of the patella
According to the not significant differences for the clinical outcomes between group 1 and 2 we routinely retain the patella. Patellar resurfacing is done only in selective cases.
Total knee replacement is a complex procedure, and the patella resurfacing could complicate more the evolutions of this complex procedure.


BIBLIOGRAPHY
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