Individualizing the Tibial Tubercle-Trochlear Groove Distance: Patellar Instability Ratios That Predict Recurrent Instability

Christopher L. Camp, Mark J. Heidenreich, Diane L. Dahm, Michael J. Stuart, Bruce A Levy, Aaron Krych

Research output: Contribution to journalArticle

22 Citations (Scopus)

Abstract

BACKGROUND: Patients with patellar instability and a tibial tubercle-trochlear groove (TT-TG) distance ≥20 mm may be candidates for distal tubercle realignment surgery. Although this variable has proven valuable in predicting recurrent dislocations, it is not individualized to patient size, bony structure, or patellofemoral mechanics.

PURPOSE: To develop a patellar instability ratio (PIR) that predicts the risk of recurrent instability based on the TT-TG distance to patient-specific anatomy.

STUDY DESIGN: Cohort study; Level of evidence, 3.

METHODS: On magnetic resonance imaging scans of 59 knees with patellar instability, the TT-TG distance, tibial tubercle-posterior cruciate ligament (TT-PCL) distance, sagittal patellar length (PL), sagittal trochlear length (TL), axial patellar width (PW), and axial trochlear width (TW) were calculated by 2 observers in a blinded and randomized fashion. Patients were divided into 2 groups: those with a single dislocation and those with multiple (≥2) dislocations. The ability of the TT-TG and TT-PCL distances as well as the 8 different ratios to predict recurrent instability was assessed by calculating odds ratios (ORs), sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for each measure.

RESULTS: Twelve knees (20%) experienced a single dislocation, while 47 (80%) sustained multiple dislocations. A TT-TG distance ≥20 mm was predictive of recurrent instability, with a sensitivity, specificity, and PPV of 21%, 100%, and 100%, respectively. The OR for TT-TG ≥20 mm was 5.38 (P = .29), while the highest ORs for recurrent instability were noted for a TT-TG/PW ≥0.4 (OR, 7.37; P = .02) and a TT-TG/TW ≥0.5 (OR, 8.88; P = .04). The sensitivity, specificity, and PPV of a TT-TG/PW ≥0.4 were 62%, 83%, and 94%, respectively, while those of a TT-TG/TW ≥0.5 were 45%, 92%, and 95%, respectively.

CONCLUSION: Two novel PIRs (TT-TG/TW and TT-TG/PW) were identified and found to more effectively predict recurrent instability than the TT-TG distance alone. Each ratio takes into account patient-specific anatomy and can be measured in an accurate and reliable fashion by clinicians. These PIRs are a step toward overcoming some of the limitations of using the TT-TG distance in isolation. Further investigation into the clinical applications and utility of the TT-TG/TW is warranted.

Original languageEnglish (US)
Pages (from-to)393-399
Number of pages7
JournalAmerican Journal of Sports Medicine
Volume44
Issue number2
DOIs
StatePublished - Feb 1 2016

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Odds Ratio
Posterior Cruciate Ligament
Sensitivity and Specificity
Knee
Anatomy
Mechanics
Cohort Studies
Magnetic Resonance Imaging

Keywords

  • patellar instability
  • patellar width
  • ratio
  • tibial tubercle–trochlear groove distance
  • trochlear width

ASJC Scopus subject areas

  • Medicine(all)
  • Orthopedics and Sports Medicine
  • Physical Therapy, Sports Therapy and Rehabilitation

Cite this

Individualizing the Tibial Tubercle-Trochlear Groove Distance : Patellar Instability Ratios That Predict Recurrent Instability. / Camp, Christopher L.; Heidenreich, Mark J.; Dahm, Diane L.; Stuart, Michael J.; Levy, Bruce A; Krych, Aaron.

In: American Journal of Sports Medicine, Vol. 44, No. 2, 01.02.2016, p. 393-399.

Research output: Contribution to journalArticle

Camp, Christopher L. ; Heidenreich, Mark J. ; Dahm, Diane L. ; Stuart, Michael J. ; Levy, Bruce A ; Krych, Aaron. / Individualizing the Tibial Tubercle-Trochlear Groove Distance : Patellar Instability Ratios That Predict Recurrent Instability. In: American Journal of Sports Medicine. 2016 ; Vol. 44, No. 2. pp. 393-399.
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title = "Individualizing the Tibial Tubercle-Trochlear Groove Distance: Patellar Instability Ratios That Predict Recurrent Instability",
abstract = "BACKGROUND: Patients with patellar instability and a tibial tubercle-trochlear groove (TT-TG) distance ≥20 mm may be candidates for distal tubercle realignment surgery. Although this variable has proven valuable in predicting recurrent dislocations, it is not individualized to patient size, bony structure, or patellofemoral mechanics.PURPOSE: To develop a patellar instability ratio (PIR) that predicts the risk of recurrent instability based on the TT-TG distance to patient-specific anatomy.STUDY DESIGN: Cohort study; Level of evidence, 3.METHODS: On magnetic resonance imaging scans of 59 knees with patellar instability, the TT-TG distance, tibial tubercle-posterior cruciate ligament (TT-PCL) distance, sagittal patellar length (PL), sagittal trochlear length (TL), axial patellar width (PW), and axial trochlear width (TW) were calculated by 2 observers in a blinded and randomized fashion. Patients were divided into 2 groups: those with a single dislocation and those with multiple (≥2) dislocations. The ability of the TT-TG and TT-PCL distances as well as the 8 different ratios to predict recurrent instability was assessed by calculating odds ratios (ORs), sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for each measure.RESULTS: Twelve knees (20{\%}) experienced a single dislocation, while 47 (80{\%}) sustained multiple dislocations. A TT-TG distance ≥20 mm was predictive of recurrent instability, with a sensitivity, specificity, and PPV of 21{\%}, 100{\%}, and 100{\%}, respectively. The OR for TT-TG ≥20 mm was 5.38 (P = .29), while the highest ORs for recurrent instability were noted for a TT-TG/PW ≥0.4 (OR, 7.37; P = .02) and a TT-TG/TW ≥0.5 (OR, 8.88; P = .04). The sensitivity, specificity, and PPV of a TT-TG/PW ≥0.4 were 62{\%}, 83{\%}, and 94{\%}, respectively, while those of a TT-TG/TW ≥0.5 were 45{\%}, 92{\%}, and 95{\%}, respectively.CONCLUSION: Two novel PIRs (TT-TG/TW and TT-TG/PW) were identified and found to more effectively predict recurrent instability than the TT-TG distance alone. Each ratio takes into account patient-specific anatomy and can be measured in an accurate and reliable fashion by clinicians. These PIRs are a step toward overcoming some of the limitations of using the TT-TG distance in isolation. Further investigation into the clinical applications and utility of the TT-TG/TW is warranted.",
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T2 - Patellar Instability Ratios That Predict Recurrent Instability

AU - Camp, Christopher L.

AU - Heidenreich, Mark J.

AU - Dahm, Diane L.

AU - Stuart, Michael J.

AU - Levy, Bruce A

AU - Krych, Aaron

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N2 - BACKGROUND: Patients with patellar instability and a tibial tubercle-trochlear groove (TT-TG) distance ≥20 mm may be candidates for distal tubercle realignment surgery. Although this variable has proven valuable in predicting recurrent dislocations, it is not individualized to patient size, bony structure, or patellofemoral mechanics.PURPOSE: To develop a patellar instability ratio (PIR) that predicts the risk of recurrent instability based on the TT-TG distance to patient-specific anatomy.STUDY DESIGN: Cohort study; Level of evidence, 3.METHODS: On magnetic resonance imaging scans of 59 knees with patellar instability, the TT-TG distance, tibial tubercle-posterior cruciate ligament (TT-PCL) distance, sagittal patellar length (PL), sagittal trochlear length (TL), axial patellar width (PW), and axial trochlear width (TW) were calculated by 2 observers in a blinded and randomized fashion. Patients were divided into 2 groups: those with a single dislocation and those with multiple (≥2) dislocations. The ability of the TT-TG and TT-PCL distances as well as the 8 different ratios to predict recurrent instability was assessed by calculating odds ratios (ORs), sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for each measure.RESULTS: Twelve knees (20%) experienced a single dislocation, while 47 (80%) sustained multiple dislocations. A TT-TG distance ≥20 mm was predictive of recurrent instability, with a sensitivity, specificity, and PPV of 21%, 100%, and 100%, respectively. The OR for TT-TG ≥20 mm was 5.38 (P = .29), while the highest ORs for recurrent instability were noted for a TT-TG/PW ≥0.4 (OR, 7.37; P = .02) and a TT-TG/TW ≥0.5 (OR, 8.88; P = .04). The sensitivity, specificity, and PPV of a TT-TG/PW ≥0.4 were 62%, 83%, and 94%, respectively, while those of a TT-TG/TW ≥0.5 were 45%, 92%, and 95%, respectively.CONCLUSION: Two novel PIRs (TT-TG/TW and TT-TG/PW) were identified and found to more effectively predict recurrent instability than the TT-TG distance alone. Each ratio takes into account patient-specific anatomy and can be measured in an accurate and reliable fashion by clinicians. These PIRs are a step toward overcoming some of the limitations of using the TT-TG distance in isolation. Further investigation into the clinical applications and utility of the TT-TG/TW is warranted.

AB - BACKGROUND: Patients with patellar instability and a tibial tubercle-trochlear groove (TT-TG) distance ≥20 mm may be candidates for distal tubercle realignment surgery. Although this variable has proven valuable in predicting recurrent dislocations, it is not individualized to patient size, bony structure, or patellofemoral mechanics.PURPOSE: To develop a patellar instability ratio (PIR) that predicts the risk of recurrent instability based on the TT-TG distance to patient-specific anatomy.STUDY DESIGN: Cohort study; Level of evidence, 3.METHODS: On magnetic resonance imaging scans of 59 knees with patellar instability, the TT-TG distance, tibial tubercle-posterior cruciate ligament (TT-PCL) distance, sagittal patellar length (PL), sagittal trochlear length (TL), axial patellar width (PW), and axial trochlear width (TW) were calculated by 2 observers in a blinded and randomized fashion. Patients were divided into 2 groups: those with a single dislocation and those with multiple (≥2) dislocations. The ability of the TT-TG and TT-PCL distances as well as the 8 different ratios to predict recurrent instability was assessed by calculating odds ratios (ORs), sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for each measure.RESULTS: Twelve knees (20%) experienced a single dislocation, while 47 (80%) sustained multiple dislocations. A TT-TG distance ≥20 mm was predictive of recurrent instability, with a sensitivity, specificity, and PPV of 21%, 100%, and 100%, respectively. The OR for TT-TG ≥20 mm was 5.38 (P = .29), while the highest ORs for recurrent instability were noted for a TT-TG/PW ≥0.4 (OR, 7.37; P = .02) and a TT-TG/TW ≥0.5 (OR, 8.88; P = .04). The sensitivity, specificity, and PPV of a TT-TG/PW ≥0.4 were 62%, 83%, and 94%, respectively, while those of a TT-TG/TW ≥0.5 were 45%, 92%, and 95%, respectively.CONCLUSION: Two novel PIRs (TT-TG/TW and TT-TG/PW) were identified and found to more effectively predict recurrent instability than the TT-TG distance alone. Each ratio takes into account patient-specific anatomy and can be measured in an accurate and reliable fashion by clinicians. These PIRs are a step toward overcoming some of the limitations of using the TT-TG distance in isolation. Further investigation into the clinical applications and utility of the TT-TG/TW is warranted.

KW - patellar instability

KW - patellar width

KW - ratio

KW - tibial tubercle–trochlear groove distance

KW - trochlear width

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