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ID naloge: 71 Letnik: 1999 Predmet: ortopedija
Primerjava biomehanskega statusa displasticnih in zdravih kolkov
Avtor: Blaž Mavcic
Mentor: doc. dr. Veronika Kralj-Iglic, dipl. ing. fizike
Somentor: doc. dr. Vane Antolic, dr. med., asist. mag. Dragica Smrke, dr. med
Izhodišca: Za kolcno displazijo pri odraslih so znacilne morfološke in mehanicne deformacije v kolcnem sklepu, ki dolgorocno povzrocajo obrabo sklepnega hrustanca in nastanek osteoartroze. Poleg klinicnega in rentgenološkega ocenjevanja displasticnih kolkov so za boljšo oceno statusa kolka pomembni tudi biomehanski parametri, zlasti maksimalne tlacne napetosti, ki se razvijejo v kolcni plasti. Predhodne raziskave so že osnovale metodo za ocenjevanje kolcne displazije na podlagi dolocanja tlacnih napetosti, ki pa še ni bila klinicno preizkušena.
Namen naše naloge je bil ugotoviti, ali imajo displasticni kolki vecje maksimalne tlacne napetosti v kolcni plasti kot zdravi kolki. Ker se tlacnih napetosti v klinicni praksi ne da izmeriti neposredno, smo si pri oceni tlacnih napetosti pomagali z rentgenskimi posnetki kolkov, iz katerih izracunamo tlacne napetosti z matematicnim modelom kolka pri stoji na eni nogi. Pri tem nas je tudi zanimalo, v kateri biomehanskih parametri, potrebni za izracun tlacnih napetosti (kot lateralnega pokritja kolcne glavice, radij kolcne glavice, velikost in nagib rezultantne kolcne sile), se displasticni kolki razlikujejo od zdravih.
Preiskovanci in metode: V raziskavo smo vkljucili rentgenske posnetke 56 displasticnih kolkov, ki so bili zaradi kolcne displazije operirani na Ortopedski kliniki v Ljubljani v letih 1988-1993. Kontrolno skupino zdravih kolkov je predstavljalo 60 kolkov preiskovancev, ki so se v letih 1988-1996 zdravili na Klinicnem oddelku za travmatologijo zaradi zloma kolcnega vratu (v raziskavo so vkljuceni le nepopkodovani kolki). Antero-posteriorne rentgenske posnetke kolkov smo obrisali, prenesli v digitalno obliko s posebnim graficnim sistemom ter z dodatnim racunalniškim programom avtomatsko izracunali vrednosti maksimalnih tlacnih napetosti in ostalih biomehanskih parametrov v obravnavanih kolkih na podlagi matematicnega modela kolka.
Rezultati: Dobljeni rezultati so pokazali, da so maksimalne tlacne napetosti v displasticnih kolkih (mediana = 4,36 kPa/N) pomembno vecje kot v zdravih kolkih (mediana = 1,72 kPa/N). Razlika je statisticno pomembna (P < 0,0001). K temu najvec prispevata statisticno pomembno zmanjšan kot lateralnega pokritja kolcne glavice in statisticno pomembno zmanjšan nagib kolcne sklepne sile pri displasticnih kolkih. V radiju kolcne glavice med displasticnimi in zdravimi kolki ni pomembne razlike. Displasticni kolki imajo statisticno pomembno vecjo kolcno silo, vendar to ne vpliva bistveno na razlike v tlacni napetosti.
Izboljšali smo metodo za ocenjevanje displazije kolka pri odraslih, tako da je z avtomatskim racunalniškim programom možno analizirati rentgenske posnetke kolkov z razlicnimi nagibi kolcnega vratu in razlicnimi nagibi stegnenice.
Zakljucki: Maksimalna tlacna napetost doseže v displasticnih kolkih pomembno vecje vrednosti kot v zdravih kolkih in torej lahko služi kot pomemben parameter pri ocenjevanju displazije kolka. Empiricno pogosto uporabljeni parameter pri ocenjevanju displazije, lateralni kot pokritja kolcne glavice, se v obeh populacijah ravno tako pomembno razlikuje. Pri mejnih vrednostih tega kota pa pride bolj do izraza vpliv ostalih biomehanskih parametrov na velikost tlacnih napetosti (velikost in nagib rezultantne kolcne sklepne sile, )
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[Abstract / English version]
Comparison of the biomechanical status in dysplastic and healthy hips
Author: Blaž Mavcic
Mentor: doc. dr. Veronika Kralj-Iglic, dipl. ing. fizike
Co-mentor: doc. dr. Vane Antolic, dr. med., asist. mag. Dragica Smrke, dr. med
Outline: Dysplastic hip joint is morphologically and mechanically deformed, which may in the long term result in joint cartilage degeneration and ostheoarthrosis development. Clinical, radiographic, but also biomechanical assessment are important in the examination of dysplastic hips, the most important biomechanical parameter in evaluation of the hip status being the maximal stress that develops in the weight bearing surface of the hip. The method used for hip stress evaluation has been developed previously, but has so far never been clinically tested.
The aim of our work was to evaluate whether dysplastic hips have higher maximal stress values than normal healthy hips. As direct hip stress measurements are not possible, hip forces and stresses were computed on the basis of antero-posterior rentgenograms of the patients in combination with mathematical models of the one-legged stance. The purpose of our work was also to elucidate which biomechanical parameters, necessary for the hip stress computation (the Wiberg angle, femoral radius, magnitude and direction of the resultant hip force) differ significantly in dysplastic and healthy hips.
Patients and methods: The research group consisted of 56 dysplastic hips, which were operated at the Orthopedic clinic in Ljubljana between 1988-1993. The control group consisted of 60 hips of patients that have undergone medical treatment at the Traumatological clinic in Ljubljana between 1988-1996 due to trauma of the femoral neck (we only examined the healthy, undamaged hips). Contours of antero-posterior rentgenograms of the selected patients were made and then transformed into digital form which enabled further automatic computerized calculation of hip stresses and other biomechanical parameters of the hip on the basis of mathematical models.
Results: Results show that the maximal hip stress attains significantly higher values in dysplastic hips (median = 4,36 kPa/N) than in normal healthy hips (median = 1,72 kPa/N). The difference is statistically significant (P < 0,0001). This is mostly due to the considerably and statistically significantly reduced Wiberg angle and due to considerably and statistically significantly reduced hip-resultant-force inclination. There was no significant difference in femoral radius between dysplastic and healthy hips. The hip-resultant-force magnitude was significantly different in both hip populations, but it did not affect the difference in stresses between dysplastic and healthy hips.
We improved the method for hip dysplasia evaluation in adults so that the automatical computerized calculation can be performed for different femoral neck inclinations and different femoral inclinations with respect to the sagittal plane.
Conclusions: Maximal hip stress in the hip weight bearing area attains importantly higher values in dysplastic hips than in healthy hips and could therefore serve as an important parameter in hip dysplasia evaluation. The Wiberg angle is empirically often used as the evaluation parameter and was significantly different in both hip populations. However, in borderline values of the Wiberg angle other biomechanical parameters have larger influence on the hip stress values (magnitude and direction of the hip resultant force).
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